There are two mutually exclusive parts to the 8915-E.
One part is if you want to split the distribution into three parts. The checkbox is a binary choice.
That is, you either want to split it over three years or you don't.
The second part is if you repaid the distribution and if you did, how much.
The repayment made (if any) offsets the result of your distribution choice.
You can split without repaying or you can repay without splitting or you can split and repay.
As I have been suggesting, download the 8915-E form from the IRS and fill it out manually so you can see how it works.
This form only determines how much of your distribution is taxable this year.
Taxes already paid vs taxes due are calculated as part of your total tax return (in its entirety).
