Partial Mash/full boil calculation question

I am doing the AHS Fuller's London Porter kit tonight. It is a partial mash kit and I am going to do a full boil in my turkey fryer.

Here are the ingredients:
5.5 amber
2.5 pale malt
1 60l
.5 Malto-Dextrine
.75 chocolate
.25 victory malt
1.75 fuggles
.25 fuggles (15m)

Here is what Beersmith says when I scaled to 5 gallons:
5.5 amber
2.5 pale malt
1 60l
.5 Malto-Dextrine
.75 chocolate
.25 victory
.9oz fuggles
.1 fuggles

The IBU is only 14.4 and the style scale for a robust porter is 25-55. 14.4 seems really low. Does that seem right for a Fuller's Porter? I am thinking that maybe the % is off in beersmith for the Fuggles I have (BS is 4.5, I'm at work so I'm not sure what they are on the package).

Thanks

FYI: if I use the full amount of Fuggles in the full boil the IBU is 27.9.

I emailed AHS and they calculated the IBUs at 28 which is what I have for 5 gallons and using all of the hops. The recipe is for a 2.5 gallon boil. Something is not right here. It is looking like I should include all of the hops with my full boil even though I thought I'd be using less (about half when scaled in beersmith). Hmm...