I think I figured it out using the instructions, provided by the IRS, for Form 8379. As per the instructions, for line 20,
"These are on the lines of your return where you entered estimated tax payments, the amount applied
from your previous year's tax return, and amounts you paid with an extension to file (Form 2350 or
Form 4868)."
I'm fairly certain that line 64 of the 1040 is what is entered for 19 for (a) and (b), and line 65 from the 1040 is what would be entered for line 20. As my entire Payments section of my MFJ return was just line 64 of the ~16k, I would have 0 for (a), (b) and (c) of line 20...
Hopefully that is accurate...
