Visually, F is longer than P2 but as far as fit goes, I don't feel much of a difference. I have a pretty easy to fit foot, however, so your experience with heel support may be different. I size up half a size, however, from P2 and F to U.
Thanks Gyasih but I really didn't start at 0. The newest additions are really more of a turbo boost. Here is what I already had from Vass:Burgundy F; Dark Brown F; Antique Cognac UAntique Cognac F; Black F; Dark Cognac F; Oxblood P2 (not really certain why I went with P2 rather than F),