After reading over the 1040X and 843 more closely I think I'm of the mind that Form 843 is the way to go. With the 1040X I wouldn't be changing a single column, except for at the very bottom where I'm supposed to enter the amount of my refund as adjusted by the IRS, and what I expect my new refund to be. And there is certainly the information in the 1040X instructions that secondcor521 pointed out, and it is a refund of a penalty that we're seeking. I'm able to fill out Form 843 in a manner that makes it feel like a more complete document that I would be able to with Form 1040X. I'll mail in Form 843, along with my now completed Form 2210 and see what happens. I'll be sure to report back my results.