Isomerization of hop oils is said to increase in a wort of lower specific gravity than the same amount of hops in a higher gravity wort. I have read from 5% to 10% greater isomerization in the lower gravity wort. I don’t have any experience with this. I’m unable to do full 5 gallon boils.
A recipe calculator, like the free one here, may give you an idea of how the IBUs may increase with a full boil compared to a partial boil with your recipe.
