Beersmith giving me some wild numbers for full boil/late LME addition

Ok, so im doing the AHS stella clone, and it automatically comes with LME (Not typically a fan of working with LME) but anyways, I want to try and max out my performance on this one so i figure i'll do a late addition to avoid malliard reactions and a darker color. Also, i always do full boils because i think they have a serious flavor impact.

So anyways, the recipe calls for 2 oz of Saaz at 60, 1 oz at 15, and another oz at 5 min. Well, I make the adjustments on beersmith for full boil and late LME addition, and according to beersmith, to hit 23 IBU's I need to only put in .5 oz of saaz at the start of the boil.

thats only 25% of the bittering hops the recipe calls for. Thats a pretty huge deviation from the recipe, so i wanted some opinions here before I get crazy with the hop additions.

What do you have for 'batch-size' and equipment? Keep in mind you are still getting some utilization/isomerization at 15/5 but not much. So most of it will be from the 60 minute addition, so its not too far off.

I just punched it into my Beersmith and with a 4% AA Saaz I would get 24.6 IBUs by following what you gave me. Make sure your batch-size and equipment are accurate.