The shorter is better thing only works if it's so short, or you're so tall, that your entire upper shoulders, neck, and head are out "in the wind" so are not subjected to the turbulence behind the windshield. Kinda defeats the purpose of the windshield, IMO.
There are three options: Ride the bike with your head bobbling around like one of those things people put on the hat rack of their cars; Get one shorter so that your entire neck/head are totally exposed to the wind flow (and eat bugs, rocks, rain, and other road debris); Get a windshield that is the proper height for YOU by measuring carefully.
It is a decision about function over form, period. You are much further back from the shield on a RG, so windshield height is much more critical in eliminating turbulence. A full face or flip face helmet will help matters as well.