If you only use lower straps, and have them just barely tight enough that they stay up, there is no cutting into the back of knees. The strap should be well below the knee, with only the shape of your calf holding it up. Thick padding not only makes it more comfortable for the knee, but by sinking into it some, the strap only becomes looser once you're on your knees.

Top straps are only good for being uncomfortable. Ones in pants don't stay where you need for them to if you need to move side to side.