I think the most important part of having a consistant grip is that once you are positioned to keep it there by aplying pressure with your drawing arm.

Avoid holding the bow with your bow hand and THEN loosening the grip once you are at full draw.

Achieve the grip you want - with loose fingers not holding the riser - pull on the string to get pressure before you draw - then go through with the shot.

Any alteration of the grip at full draw WILL lead to inconsistant shots.