Page 1
The deck mount roller has a mounting plate 50mm lower than the top lid all the way down the length of the DMR on the front and back so the unit can be mounted on or under a frame while still having decking/paving come up to the top of the unit.
Page 2
This is of no concern for normal above ground rollers as the roller is picking up, or pulling the cover up and out of the pool. With the DMR’s the cover is being pulled along the ground, meaning the edges are being pulled into the corners not out of them.