My email paid off and I'm meeting up with the Honda guru this weekend.

I don't see how anyone could make a recommendation on intake length without knowing the exact cam timing.
Most of the formulas out there are outdated.Hes using wave tuning software and computational fluid dynamics to arrive at the starting point for intakes.
The only thing I can share with you guys is to make a test intake manifold that you can shorten 1/4" at a time and test.