The topper for my 42 inch deep 12 ft long slide collects water (6,048 sq in). The other two do not collect water, one is 33 inches deep 14 feet long (5,544 sq in), the other is 42 inches deep, but only 5 ft 5 inches long (2,730 sq in). My guess is the combination of depth and length is why the one collects water.
The mounting side on the trailer is about four inches higher on each slide topper. There appears to be equal tension on all three factory installed toppers. There is almost no flapping noise in strong gusty winds.
I took a little 3/4 inch PVC and made a 12 foot long 'ridge' that I insert between the top of the slide and the topper. Since I have a bumper pull TT, I can easily reach the top of that slide from the trailer door and the rear ladder to insert the ridge assembly (yes it's is in three pieces so it is easy to store). It would be an unacceptable pain to do that if I have a 5er or motorhome that was higher above the ground.
I don't put it out all the time, only on long stays, or if heavy rain is forecast.