The size of the PCI is affected by the vision rating of the hitter and the K/9 of the pitcher. Shape is affected by contact and power. Edit a few players to be extremes and you can see the changes. The center does feel like it is meant to be the "sweet spot" of the bat although I've hit long home runs with the ball well off the center horizontally. Vertically it sort sort of resembles the barrel in that high can be fly ball and low can be ground ball, but I've had hits where that isn't completely true. Hopefully if anything the precision input will let people know where on the PCI you really want to line up. For me it's usually just above the middle vertically and middle horizontally.