I don't understand the TurboTax checkbox for an IRA 1099-R distribution being 'all' or 'part' of the RMD. How do I decide which to check?

For example, suppose I have 2 IRAs, a big one and a small one.  The holding institutions (different) informed me that I needed to take $10000 from the big one and $2000 from the small one. ( I know that I can consider all IRAs as one for meeting the RMD, and therefore take the $12K from a single account.) But suppose I needed more money, so I took $12000 from the big one and an additional $12000 from the small one.When I get to this checkbox in TT, I can correctly answer 3 different ways: "all" the RMD came from the small IRA and none for the big one, 'all' from the big IRA and none from the other, or 'part' from both. Is there any difference? Is one of these choices any better?