I've taken to insetting a piece of capstrip material (1/16" X 1/4" or so) flush with the top of the rib at the polyhedral break to give a little more surface area to stick to. (do it on both inboard and outboard sides of the rib) I've had a problem with covering lifting from an un-widened rib even if it was stuck down smoothly to start with.

It also might be a good idea to use your iron to shrink the covering in that area rather than a heat gun... it's easier to control where the heat goes with the iron.