I don't want to beat a dead horse, Tobin, but: Not all people complain even when encountering a problem, not least because a newer diver might not understand the problem or might blame themselves or might stop diving or might dive once a year, etc.
I bought one of my two short DSS plates on the aftermarket (the SS one, which I use regularly with singles and doubles--love it; the Kydex one I bought directly from you--haven't used it yet). The aftermarket might be a form of complaint not registered directly to you. I wouldn't draw a conclusion on the head banging problem based on a combination of complaints reported to you and pop-psychology (preconditioned to expect a problem) alone.
FACT: If you are short and dive an AL80 with a direct mounted rig, you WILL bang your head on your reg unless you mount your tank very low. And if you mount your tank very low, you will feel the tank pressing down on your butt and making it difficult to arch your back.
FACT: If your butt is small and/or you are especially lithe, maybe you can still go horizontal easily enough. If you turn the tank, maybe you can reduce some head banging. If you add an STA, maybe you can minimize the problem at both the top and the bottom.
Specious Reasoning: An absence of problem preconditioning will eliminate head banging and the splint effect of a close mounted long tank on the lower body of short people.