I just had a shave with my Renaissance razor, and I experimented a bit with the grip. I think this is very much a personal preference thing, as it may actually depend a bit on the length and width of your fingers.

However, varying the grip made me notice something that I haven't thought about before: when I hold the razor as shown in the first picture of this thread, I actually use the scales to adjust the angle of the blade (by moving my middle finger on top of the scales). When holding it in other positions, the scales are less useful to me, and in some positions, they are actually quite annoying.