grip position has little to no bearing on the relative steepness of the arc. Look at Furyk: upright swing plane, strong grip. Duval in his prime: Flat Swing plane, strong grip. Hogan: extremely weak grip, extremely flat plane. Daly: very strong grip, uprightish plane, questionable mind= 2 majors and a number of tour victories. These guys all hit it pretty good. lol. Swing plane is a function of a few other variables, mainly how you are built, your height ect.
If you are concerned about the rolling of the hands having a function in the shape of the shot, I can guarantee you that there are other variables in your swing that are not working as they should. You shouldn't need the grip to produce a "rolling" effect in your downswing. The plane of the swing and path of the golf club is enough to determine ball flight. Even Leadbetter (in one of his recent golf tomes he addresses this question)amended his opinion on the necessity of having the "ideal grip". i.e. there isn't one. Sorry to all the Hogan followers!