I have a large law firm client that recently asked about mega backdoor Roth and voluntary after-tax contributions in general. I explained the ACP test issue and after a slight pause, one of the partners said, "but that can be resolved by making a company contribution instead of refunds, right?" They are actually considering corrective QMACs to let their highly paid (and, coincidentally, HPI) participants do this. Sure, it works mathematically if they don't mind spending the money, but I have to wonder if it will really work out better than adjusting their class-based profit sharing.