Beersmith, BIAB and IBUs (oh my!)

I never figured my first post here would be in the software forum, but what the heck.

I'm new to home brewing, done a few Mr Beer kits and never worried much about any numbers, no big deal. Now I have a 5 gallon setup and a copy of Beersmith. I haven't actually brewed anything with it yet, but I've been playing around in BS with some recipes, trying to figure out the process.

I'll be brewing stove top using DeathBrewer's partial mash method documented in the beginner's forum. I have a 22qt pot and an 11 qt pot, so it will be partial boil. I still haven't figured out exactly how to set my equipment profile up to reflect this setup, but I just figured I would brew a batch and see how the numbers line up and adjust from there.

Now comes my question: I've chosen a couple existing recipes on here so that I have some baseline numbers to try and match. When I enter them I I've been getting very low IBU numbers. I know that partial boils will affect that, but I'm not sure how to deal with it. As an example, I entered this recipe to see how it compared. I did convert it to partial mash (substituting DME for a bunch of the 2-row till I got under 6# of grain and a matching OG). Most of the similar recipes in that thread ended up with IBUs in the neighborhood of 100-120 or so. Beersmith gave me 57. Will the partial boil make that much difference? If I tell Beersmith to adjust to 90 IBUs it bumps the amount of hops needed way up, like double the original recipe.

I guess my question is, should I just follow the recipe as-is, or trust that Beersmith is adjusting my hops properly? I like hops, but I'd hate to end up with something face meltingly bitter. I don't really want to end up with something super sweet, either.

trust beersmith. using a smaller volume (2.5 gallons instead of 5) decreases your hop utilization in 2 ways: less overall volume to disperse the alpha acids in, and a more concentrated wort (more sugar = less room for alpha acids).

one of the best things you can do for your brewing is to move to a full-volume boil.

Unfortunately I have to stick with strictly stove top for the time being, so I don't know that I can do full boil. I did notice a 32qt tamale steamer at walmart for less than $25 when I went to buy my 22qt pot, so maybe at some point I can give it a try and see if my stove can do it.

Thanks for your thoughts on trusting Beersmith. My first attempt is going to be the Centennial Blonde so if something is off and the hops end up being too much it should still make a nice IPA at least.