I get this design, I don't think it's whack at all. Complicated, off the beaten path, yes indeed. But I certainly appreciate the desired outcome.
Try this though. Default everyone to Roth. The lower paid people are less likely to make an election (at least that's my assumption) so the default should be what is best for them,. The higher paid people will fill out a form electing pre-tax if they want to.
That's the position I took anyway when I default enrolled a plan in Roth. Their rank and file people are young and low paid. So Roth defaulting was a home-run.