The tilting of the slide box should have no effect on the topper. The topper is held taught by the spring in the roller tube it does not lock in any position but keeps constant pressure on the fabric. It may be that the spring has lost some of its tension. some folks put a pool noodle or beach ball under the fabric to get rid of the sag others put more tension on the spring.
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho