I am doing actual yield / theoretical yield of my extraction efficiency using the final volume. I should probably use run off volume.
It's weird if you look at final, because you can perceivably improve "efficiency", by boiling longer and getting less beer. Intuition tells me that is not efficient.
Your point about brewhouse efficiency is interesting though. I never even thought about it, but it does make sense. Say I have 1 gallon deadspace and someone has 1 qt, and all other things are equal I could get a higher brewhouse efficiency, yet a lower OG?