I said to enter the loss amount under Other income not already reported on a Form W-2 or Form 1099, not under Other reportable income so that it gets added to Form 1040 line 1, not to Schedule 1.
I wasn't aware that the loss on the excess contribution was excludible from income. What you do want to appear on Schedule 1 line 21 is a negative amount to offset the loss reported under Other income not already reported on a Form W-2 or Form 1099. To do that (in addition to everything else that I've already mentioned), go to Less Common Income - > Miscellaneous Income, 1099-A, 1099-C -> Other reportable income and make the loss amount you entered there a negative number.
