Do what works for you. If you dilute after the boil you are diluting gravity and bitterness. If you figure your grain and hops for the final volume instead of what you are starting with you will end up pretty close. You will likely get less bitterness because of lower utilization rates in higher gravity worts.
I cut a batch down last night. I'm just trying to crank out a basic base beer for a sour project. 10 gallon pot, started with almost 9 gallons of wort, and put 10 gallons in the fermenters. You do the math.