I don't mention it much, but a lot of golf to me is about angles. After many years of searching and teaching putting, I was able to find, what I believe, to be the "critical angles", that maximize impact on the ball for putting. Dave Pelz's "Putt Like the Pros" was a plethora of information that helped me develop my method.
If you haven't found it, at duplessisgolf.com in the "More" section, is the "Putting Routine" section. You'll find some very helpful info there. In general you can grip the putter any way you'd like as long as when it hangs, the grip/handle is slightly ahead of the putter face, and the putter face is EXACTLY 90 degrees to the path your shoulders move your arms/putter*. You can NOT change any of these angles during the stroke. If you have to have a death grip on the handle so it does not flip do it! The face must stay square and your wrists can NOT change ever during the stroke. BTW, I'll mention the arms must hang straight down to gravity (they can be bent, but can't change during the stroke) underneath your shoulders (no reaching out). Now, the next critical part ... when to make impact with the ball. This is forward ... on the upswing ... after the bottom of the swing arc ... on the "sweet spot" of the putter face. This is like an inch or two past the bottom of the arc. Experiment. This will put wonderful end over end roll on your putts for great distance control. Again, you must hit that sweet spot, and you will if you let your arms hang and don't change any thing during the swing and just let your shoulders do the work. * You can test this path by practicing your putting stroke, slightly off the ground, above a club shaft lying on the ground or any tile line in the kitchen. Something that you can look down upon to see that the club face stays perfectly square (90 degrees) to the line back and through during your stroke.
Move Less ... Get Good! DUPLESSISGOLF