Okay I ran the numbers that I had written down again and reverse engineered the spell damage. Running it through the formula matched up perfectly (with the averages of the low-high). I guess it's because they (int bonus and aero bonus) are multiplied and not added, increasing the lower number (Aero in my case) is always a more important contributor.
For anyone else who is bad at math like me, an example:
1 x 50 = 50
1 x 51 = 51
1.1 x 50 = 55
