Do you have amounts that you are reporting for July through December where your allocation is greater than 0%?
TurboTax has a list of unsupported calculations and this is one of them: Form 8962, Part IV - Allocation percentage applied to monthly amount cannot be at zero percent.
I would just leave January through June blank on Form 1095-A and only fill out the July through December amounts and allocate that using the method you have determined.
