Help! Strange attenuation issue

I'm wanting to do a Three Floyds Dreadnaught clone of sorts, and found a recipe from BYO here.

Anyways, 159 is quite a high mash temp. As such, I'm having trouble getting BeerSmith to attenuate this anywhere near what the recipe calls for (1.020).

BS says it'll stop @ 1.030 @ 159F mash, and 1.027 @ 156F mash. Any ideas what's the deal here, and how to fix this issue? Is this going to carry over into the actual brew, or is it a software issue?

I have found that the BS anticipated FG is always higher than what I shoot for and actually get. I just ignore it and go based on experience.

You can look at the yeast in beersmith and edit the yeast attenuation percentage. I believe it defaults to the "average" attenuation, but you can change this based on your experience and if you think you can get a higher attenuation. I have done this to several of the yeasts that I use frequently by looking at past recipes and finding that my average attenuation is higher than what beersmith defaults to.

See this thread:
https://www.homebrewtalk.com/f14/ipa-attenuation-383902/