Is it possible in a 401k plan with Mega Backdoor Roth to have different After-Tax contribution amount limits for each employee depending on whether they're part of the HCE or NHCE group?
For example, if an employee is in the NHCE group, then the After-Tax limit is 50% or even 90%. Else, if the employee is HCE, then the limit is just 10%. Is that even allowed in a 401k? Do common 401k trustees like Fidelity support such logic?
This may especially matter for things like Mega Backdoor Roth, where the overall limit of 58k/year/employer (as of 2021) is much higher than the total Elective Deferral limit for Pre-Tax/Roth of just 19.5k/year (as of 2021).
In turn, a single unified 30% limit for both HCEs and NHCEs may result in Actual Contribution Percentage (ACP) test for After-Tax contributions failing, because there may be more HCEs who'd participate at full 30% than there may be NHCEs.
On the other extreme, if the limit is the same 10% for everyone, then some eager NHCEs would actually be the ones most negatively impacted for no good reason as their total contribution limit would be much lower in absolute terms (10% of 50k is just 5k, whereas 10% of 150k is 15k -- compare to the 19.5k limit that's the same for everyone), and these NHCEs who may be capable of contributing 50% or more to bring the ACP averages for the whole NHCE group significantly upwards would be denied an opportunity to do so, thus keeping everyone down at the lower limit forever.
