More krausen in AG?
 

I have done 7 AG batches and 35 extract batches and think I may be noticing a pattern... Typically i will do an extract batch while mashing/sparging. in my AG batches the krausen ring is much thicker than in the extract batches when using the same yeast. (Washed yeast for both from prior batch, 48hr starter for both batches, pitched about an hr apart - so it's not the yeast). Is this just a coincidence or is something going on here? I generally am in the 75-85 % efficiency range

Protein, I am guessing that the extract is more efficiently made than your AG batches. The proteins that go into the Krausen are lesser in the extract.

Maybe a "real" scientist can refute my guess.

May have to do with the amount of free nitrogen available for yeast reproduction. AG would normally have more.