Dark Belgian (Rochefort 10 clone) help needed

So a few years back my friend's dad highly recommended that I try a Rochefort 10. After having one, I understood why it came highly recommended. Wasn't long before I decided to try making a sort of clone, just for the fun of it. In searching for a clone recipe, I found that there really isn't much out there for it. The recipe I found that seemed to be the most reasonable was from Stout Fellow. Of course, the recipe was listed in Metric, so I had to convert to US measurements and because at the time I was partial mashing on the stove and my ability to all grain was limited (plus the Metric amount worked out to 6.6 gallons), I cut the recipe as closely in half as I could. Then, lacking the sugars he specified, I substituted using dark Candi syrup (D-180), table sugar and light brown sugar. The result was actually quite agreeably good. The bad news is, I'm down to less than half a case and I want to brew more, but since I have the ability to make a much larger quantity this time around, I want to make either a full batch (11 gallons into the fermenters) or as close to it as I can manage. And that's where I'm getting into a dispute with BeerSmith...

So I'd like some help from ya'll to try to get this worked out so I can produce something similar to what I already made, just in a larger quantity. I spent most of the afternoon fighting with it and I'm not convinced that I'm on the right track.

First off, here's the recipe from Stout Fellow converted to U.S. measurements:
"Rochefortesque"
6.6 gallons
90 minute boil
70 minute mash @ 150.8*

13.23 # German Pilsner
1.1 # Caramel/Crystal 120L
1.32 # Special B
1.32 # Flaked Wheat
0.66 # Black Malt (specified that it may be best to use Carafa or De-Bittered)

1.1 # Demerara sugar @ 20
1.1 # Soft dark sugar @ 20

2.29 oz East Kent Golding @ 80
1.41 oz Hallertau Hersbrucker @ 10

Now, my attempt at it....
Monk's Ten - BIAB
my notes specify that I oversparged and had 4.25 gallons pre-boil and around 3.25 or so at bottling, but no other specifics on volumes

6.5 # German Pilsner
0.6 # Caramel/Crystal 120L
0.75 # Special B
0.75 # Flaked Wheat
0.36 # Debittered Black

0.6 # Table sugar (I believe I did half and half table and light brown sugar) @ 10
0.6 # Dark candi syrup D-180 @ 10

0.75 oz East Kent Golding @ 60
0.6 oz Hallertau Hersbrucker @ 10
0.4 oz Amarillo @ flameout

*Chill times were extended due to the lack of an ice bath, I just did a cold tap water bath. I also managed to fail at noting gravity readings with the exception of the FG of 1.002. In theory, my starting gravity into the fermenter should have been around 1.098 although I suspect my efficiency wasn't up to par with that prediction because it doesn't taste like it's over 9-10% ABV. IBU was supposed to be around 25.45. BeerSmith claims that what I brewed should be a 1.074 OG with 13.3 IBU which doesn't match very well with what my thoughts on the taste are.


Now, when I put Stout Fellow's recipe in Beersmith using the generic BIAB brew settings and tell it to scale to my equipment settings, I get the following.

21 # 14 oz Pilsner
2 # 3 oz Flaked Wheat
1 # 15.6 oz Special B
1 # 13.7 oz Demerara (substituted to table sugar)
1 # 11.1 oz Soft dark sugar (substituted to D-180 syrup)
1 # 10.3 oz Caramel 120
15.8 oz Debittered Black

3.74 oz EKG @ 60
2.30 oz Hallertau @ 10

OG - 1.081
IBU - 27.4

I should mention, my current equipment is set for a target batch of 11 gallons into the fermenters. I'm pretty sure I have my current equipment settings dialed in pretty close. I used to use a free program (Brewers Friend) and write out all of my recipes after building them. I also used an app on my phone that gave me similar results to Brewers Friend. When I transfer either of those recipes into BeerSmith using my current equipment settings, everything comes out pretty much dead on (all three agree). Where it gets strange is before I got my current equipment, I could never get all three programs to agree (Brewers Friend and the app would agree, but BeerSmith had other ideas) and I could never figure out what the problem was.

Telling BeerSmith to scale my original results in numbers not too far below Stout Fellow's recipe that I scaled, but it retains the pitifully low IBU number of 13.3 and still gives me an OG of 1.074.

18 # 4.8 oz Pilsner
2 # 2.9 oz Special B
2 # 1.8 oz Flaked Wheat
1 # 15 oz Soft dark sugar (substituted to D-180 syrup)
1 # 14 oz Demerara (substituted to table sugar, will divide between table and light brown)
1 # 11.9 oz Caramel 120
1 # 0.8 oz Debittered Black

1.44 oz EKG @ 60
1.16 oz Hallertau @ 10
0.77 oz Amarillo @ 5 (to adjust for the slow chill)

Now, I tried tweaking those numbers to be more like the ones from Stout Fellow and this is what I came up with, but I'm not sure if I'm on the right track or not.

22 # Pilsner
2 # 3 oz Special B
2 # 2 oz Flaked Wheat
2 # D-180 candi syrup
2 # light brown sugar
1 # 12 oz Caramel 120
1 # Debittered Black

3.25 oz EKG @ 60
2.25 oz Hallertau @ 10
1 oz Amarillo @ 5

OG - 1.084
IBU - 25.8

As above, these are numbers for an 11 gallon batch into the fermenters

So I'm at a bit of a loss as to exactly how to handle this. I don't know if I'm on the right track with tweaking the numbers or way off base. Things just don't seem to be adding up to me and I just want to brew another batch of this awesome beer.

When you scale recipes, BeerSmith gives you two options. You can scale linearly, in which all of the ingredients maintain the same percentages and ratios. The default method is to match the specs of the original recipe. In the matching format, BeerSmith may change the percentages and ratios of malts to get matching color and gravity and the amount hops to maintain IBUs.

I find when scaling a light colored beer or a very dark colored beer with modest IBUs, that matching specs is the best match. I've found that the amber to brown range is trickier and usually just scaling linearly gives me a better jumping off point. Then I can fine tune because where I want to get color and gravity change according to style in midrange beers.

I would be making recipe adjustments the same way you did for the 11 gallon batch. Especially since you're changing your sugar additions and you want to keep a certain flavor profile.

For your IBUs, you have to know which formula is being used in order to match up. I'd look at the addition amounts and AA%, then scale from that keeping the timing of the original. Once you have that baseline number, you can adjust.

I didn't know that you could have it scale linearly, that would have been what I was after I think. I finally ended up spending time tweaking the amounts until the percentages lined up and the IBUs came to the right number from the original recipe I worked from. The predicted original gravity came in higher, but I'm not really worried about that. I measured things out and ran outside to brew it yesterday while we had nice weather.

One issue that I ran into was that after I added the sugar additions, my volume increased substantially and it messed up my target finished volume. Ended up extending the boil a little to get the volume down to what I could fit in the fermenters.

I know that an 11 gallon batch sounds a little strange to some, but I try to get around 5.5 gallons in the primary so that by the time I rack to the secondary (I prefer to), and get to bottling day, I end up with 5 gallons into the bottle.

Thanks for the input though!