Here's a couple of observations:
Most people I know who are not revolver gunnies tend to grip firearms low, so that the pointing excercise does not change the normal alignment of their hand-wrist-forearm-upperarm.
1. The way you pick up a 642 'naturally'--say, off a table / display case, then juggle it in your hand to get your natural grip--is not necessarily the grip you want to adopt for good shooting in SD scenarios. Under a more realistic scenario--say from a pocket draw--even if your holster is cut right you may still not get your natural grip.
2. A high grip--one with the thumb-forefinger web up above the grip-frame transition--is the one that is most helpful is controlling recoil and that also allows for a more secure hold with a short / boot grip installed. That feels unnatural when trying to aim--but it will feel much better when point shooting.
It sounds to me like you are already starting to grip the 642 high, and that is probably a good thing. I shoot a j-frame with the CT-405 (short) grip installed. The recoil pocket does add to the grip, but it doesn't, IMO, aid in adjusting my point / 'natural grip.' I simply have practiced enough to develop new muscle memory so that my 'natural grip' has changed.
Jim H.