SG and Mash temperature, Calculation error?

Hello,
Mash profile: With a mash temperature of 64 degrees C I received an estimated SG 1013. When I changed the mash temperature in the profile to 63 degrees C, rose assumed SG to 1017. I had expected 1012 or slightly lower.
Is there a calculation error here?

Could you attach a recipe for review?

Double IPA recipe.
With 63C in first mash step Final Gravity i estimated to 1.017
Edit the mash in temp. to 64C, the Final Gravity is estimated to 1.013

I believe what it is trying to model is the drop off in fermentability when you drop below the active range for alpha-amylase.  It would appear that at 63 C, it is offset from the literature that I have which states and graphically identifies this inflection point at around 62 C.  I looked at the fermentability curve adjustment, but changing the center point for the mash FG adjustment does not change the point at which this kicks in, so I think it is not an adjustable variable.    Of course, Brad may be using a different book for modeling the enzyme activity that what I am looking at.

Thank you very much. Always something new to learn