Got pkgs mailed...asked re: FRE's and was told that as long as the flap was able to seal it I could fill it...It didn't have to be "flat" Bulge OK as long as it was sealed initially with it's own adhesive flap and the package was not altered.
There have been occassions when the corner of the flap looked like it might "catch" on something, at which time they tape it down without problem.