Beersmith does not adjust the ibu values of the pre aroma steep hops when you do an aroma steep. I suppose you could duplicate the boil hops as a steep addition in the software, but I don't bother with that.
If you steep in the 140-160 range, not much bitterness is added from any of the hops. If you steep at a temperature less than 194F, you should adjust the steep utilization factor. The default is 50% and this is for 194F.
Don't be afraid to add 20-40ibu as a steep addition. I don't perceive much extra bitterness from a 60 minute steep at 160F. For example, the beer I'm drinking now calculates 87ibu. 20ibu is from the steep. Extra ibu from the boil hops being steeped was not calculated. The beer is not rough at all. I would call it medium smooth bitter, but still pretty hoppy and flavorful. If I drank it blind and had to guess the ibu, I'd guess 50.