IBU and boil volume

Brad,

I was playing around in Beersmith and noticed that if I did a 28L boil, boiling off 7L in 90 min, then adding that 7L back as topup (this is about what happens in my system), I get the same IBU estimate as if I tell Beersmith that my evap. rate is 0%/hour and no topup.  Seems like doing it the high boiloff/high topup method would give me less bitterness due to the wort being denser during the boil.

Is this accounted for somewhere?

I'm using Tinsenth.

David

David,
 It uses the starting boil volume as the basis, so this is why it does not change.

Cheers,
Brad