All Grain/PM Over thinking??

I have a couple years of Extract brewing under my belt to include a couple PM's. I have always done a 3gallon boil and use BeerSmith to work out my recipes. I now have a nice new 10gal pot, immersion chiller, and my trusty 5gal mash tun that I used for my PM's. So here is my question:
In Beersmith doing a 3 gallon 60min boil, 5gal final volume(top off) the IBU's are calculated. Now if I go all grain or even a PM and my final volume will be 5 gal but my starting boil volume could be up to 6-7 gallons. What volume do you use in BeerSmith so that the bitterness gets calculated correctly. The volume of runnings at the start of the boil I assume??? I want to make sure any new AG or PM brews come out tasting as good and as balance as my 3gal boil extract brews.

The volume you put into the box in the upper left corner area above the recipe details is the volume you want going into the fermenter. I use 5.5 gallons, so that if I lose 1/2 gallon to fermenter trub I have a final 5 gallons packaged.

Under the equipment tab you can enter how much you anticipate losing to kettle trub, the boil off rate (it's in %/hour), amount lost in the lauter tun, volume change due to cooling (4%), etc. So Beersmith will calculate your pre-boil volume for you based on what values you enter (that'll typically be in the 7.5 to 8 gal range for me), and will use that pre-boil volume to do the IBU calculations.