I have two different brands of aftermarket C6 converters on hand, measured like your picture I get about .515” - .531” on one, and about .421” - .437” on the other.
It seems I have heard reports of the pilot hole in some aftermarket crankshafts being shallow, maybe someone can confirm if that’s an issue? I have used both these converters, but with factory Ford cranks & flexplates.
I’ll edit to add - I imagine an aftermarket SFI flexplate of thicker material and possibly different shape could affect the assembly too.