I have been working to tune BeerSmith 3 to support BIAB with a sparge. I am using the Mobile version, but I think the basic features are about the same. The software seems to be lacking a feature or two to make this fairly common practice easier.
As mentioned by Oginme, I found I had to tweak my Grain Absorption default values. At least in the Mobile version, there are values "Grain Absorption" and "BIAB Grain Absorb". I changed these both to 0.4 fl oz/oz to match what I measured (which was 0.5 gal for 10 lbs of grain). Before I did this change, I had an extra 0.5 gal of water in my kettle. This likely varies based on your process and crush size.
With that change made, I then have had the best luck setting the process to look like I am doing a Fly Sparge (with BIAB unchecked and Batch Sparge unchecked). I uncheck "Use Equal Batches", but that should not matter. I have "Drain Tun Before Sparge" unchecked, but I don't know what impact that has.
I then note the total water volume (usually around 7.5 gal) and tweak the "Water/Grain Ratio" so that I have 2 to 3 gals of sparge water.
The suggestion from the Brulosophy video to uncheck "Adjust Temp for Equipment" seems like a good idea that I will play with. I have been confused by that setting, as well as "Mash Tun Weight" and "Tun Specific Heat", but it it seems that these values do not matter if the "Adjust" option is unchecked.
Anybody else got tips or feedback?