What availability to plan for in highest modulation?

Very new to this forum, apologies if I am repeating the same question that was answered earlier.

I have been planning microwave links for a while and I am interested to know what is your take on availability in lowest and highest modulation.

For most of the links, though I am getting 5 9’s for the lowest modulation (e.g. 4QAM), I am getting around 3 9’s for the highest modulation (e.g. 4096QAM). I am using Adaptive Modulation (ACM).

My query: Is it necessary to get 5 9’s for the highest modulation too or can I strive to get 5 9’s in the lowest modulation only and try to get the best possible availability as I go higher?

I am planning in the USA, does FCC have any recommendation on this?

Please let me know if you need more information to answer the query.