Having the rear a little higher than the front (an inch or two is fine) is best for cutting faster and clearing the clippings out from under the deck; the grass is getting cut at the front of cutter. Having the front a little higher than the rear is best for mulching the clippings smaller; the grass gets cut at the front of the cutter and again at the back. Just depends on how you want to do it. Personally, I did it with the rear higher.