I installed a carefree and have the same issue.
There are many versions of slide out design and carefree advises that if the slide has a trim band around it of a certain size to buy the longer version of the mounting hardware. Which I did as do many installers I'm sure.
Turns out had I bought the shorter hardware there would have been plenty of slope to drain the water without puddling and it would have fit the slide just fine.
I just live with it as I'm not paying carefree for a second way overpriced bracket.
If yours is a carefree, your slide trim is of a width that will allow it to fit, and you simply cannot live with the issue, they sell a short bracket that you just screw in place of the existing one that will lower the roller tube 3 or 4 inches.
And what DownTheRoad said is a fact, I've stood in the wrong place several times, yes you would think one would learn the first time.