@tccpg289 

"The non-deductible amount immediately contributed was indeed converted."

There is no selective conversion from Trad IRA. The way to properly state this is, the amount that is the same as the undeducted contribution is converted. And now you have a pro rata taxable conversion. It's no longer "backdoor."

All balances in Trad IRA, SIMPLE IRA and SEP IRA are used in the math.

The undeducted contribution is Basis. The math on the form will compute the % of Basis in the total FMV. That % is used to compute how much of the conversion is nontaxable because it is considered to be from Basis. It also is used to update the records of how much Basis remains in the account, if the account(s) were not fully converted.