Recipe/Efficiency Adjustments

This may seem like a dumb one but I'm curious how you change your recipe for differing levels of efficiency.  For example, if a recipe assumes 65% but you, routinely achieve between 75-80% how much do you lower your grain bill to get the right starting OG.  Obviously, you could just lower the weight of the base grain until BS tells you your in the neighborhood but I'm wondering about the specialty grains as well.  Is this a linear sort of thing where if you reduce the base grain by 5%, you will also reduce all the specialty grains by the same amount? 

Thanks

WR 

If all you had was the efficiency, you could probably back into a similar recipe if you held batch size constant to theirs, and then scaled to your batch size. 

If you also had the other likely specs of SRM, OG, IBU, and even BU:GU, then I'd copy the ingredients and their percentages, trying to mimic the key stats. 

Zymurgy and BYO tend to give every recipe stat but efficiency, so when I copy a recipe from them, I benchmark to their numbers and specs, but using my efficiency and then scale to my batch size. 

Thanks for the help maltlicker.  I know BYO assumes 65% efficiency.  So, if I assume 10% greater efficiency can I reasonably decrease my grain bill by 10%?

After adjusting (or not) the batch size, I'd think so.  Changing the batch size, however, would either dilute or concentrate the gravity, IBUs, etc.  So if your system is 10% more efficient, but you made 10% more wort, those changes may net out each other and the taste would stay the same.  I believe we first want to mimic the ratio of each grain and the timing and IBU's of the hops, etc. to match the flavor of the target recipe.  I'm always scaling down to my smaller batch size, so I try to first duplicate their stats and then enter my EE% before scaling down and altering the recipe elements. 

Ironically, I was just playing with this in BS yesterday for a club education session next week, but it struck me how much the batch size changed the gravity that is achieveable, given certain efficiency percentages or amounts of grain.  Line #1 might be a typical partial-mash setup, line #2 a larger more efficient partial set up, and line #3 is my small-batch, all-grain, full-boil method.  I can make most beers under 1.060 before needing DME or sugars/syrups to boost gravity, although in smaller batches.

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I normally shoot for 5.5 gallon batches so I see your point when the recipe assumes five gallons.  I think you answered my basic question though, about changing all the grain proportionally.