As long as you've been changing hand positions frequently, no advice on prevention. Seems you've got the optimal set up. The worry is the increasing weakness in your hands. As it is becoming a serious concern, I'd park the bike for a few days. Give those nerves a rest.

Strangly, I get hand tingling riding my bent, no pressure at all. Not as bad of course as when I was on an upright. Guess it has something to do with wrist angle.