Beer Smith - Lost to Trub and Chiller

Cuerrently my new keggle does not have a diptube yet and I am leaving about 1.5gal behind. I know it's bad but I goose up the grain bill and hops to make up for it until I have the time to make a decent diptube/hopstopper.
However, i think the equipment profile in beer smith is throwing off my IBU and Gravity calcs.

I've noiticed that when I set my batchsize and my boil off% no matter what I put in for "lost to trub and chiller" I keep getting the same IBU's and gravity.
I don't know why.
Example:
7.5# Pils
1.25# White Wheat
1.25# Vienna
1oz tetnang 4.4% 70min
1oz ternang 2.4% 60min
1oz tetnang 2.4% 10min

77% Eff.
Batch Size 5.25GAL
Boil off 10.5%
Lost to trub and Chiller 1.5Gal
It calcs the same OG and IBU as when I keep everything the same and set the lost to field to 0.5gal.
does it assume trub and losses have zero no gravity and bitterness?

With my actual preboil eff% calculated at 77% the only way I could make the beersmith OG numbers match my actual OG measurement was to leave the "Lost to trub/chiller" at 0.5gal (default) and up the batch size to 6.25 gal. So I guess I have a work around, but I just thought this was weird...

i know this is super old, but i was just searching around for ways to reduce trub loss and read this ... if you change your loss to trub, i'm pretty sure you have to adjust your brewhouse efficiency inversely. when you do that, the gravity and ibu do indeed change.