When the blade is front mounted, each up and down movement of the wheels as they go over humps, into holes, etc. are exagerated at the blade. When it is in the middle position it tends more to average the wheel up and down movements. I don't know if that makes much sense, but think of a 10 foot long board, with a concrete block under one end, and another one 7 feet from the first. which leaves one end of the board sticking out about 3 feet. As either block is moved up or down, the end of the board moves more than the block, but the spot halfway between the blocks moves less than the block. When you combine this with the fact that the linkage for the lift moves the front mount blade faster than when in the middle you can also make more precise adjustments.