Deductions & credits

I found the line item now, but I still don't know the math.

 

Tax is being reduced by "Credit for prior year minimum tax. Attach Form 8801" from Schedule 3 in line 20. And with the tiny increase in charity, that credit is almost getting doubled. Hence, the bigger refund. 

 

I may have to read up on that 8801 Form now to understand the calculations.