With the exception of the 2nd and 5th photo, all of the plaids are wrapped around the body. So the weight of the plaid hanging on the back is not pulling the shoulder of the jacket backwards. The 2nd photo appears to be a "fly" plaid style and more of a photo "op" and probably a temporary situation. The 5th photo, the jacket(doublet) is likely held in place by the belt.

Since it's usually only the pipers these days that wear the plaid in a wrapped fasion, everyone else is lowering the placement of the brooch to act as a counterweight.

Just a quick observation.