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Elevate both feet. Do this to increase the range of motion. Use exercise steps or stack weight plates on the ground to gain 2-3 inches of elevation. Doing it this way increases the bottom range of motion by a few inches. Don't let your back knee hit the ground without the front hip fully flexing. This will engage the glutes even more. Do these with higher reps (between 10-20). Keep constant tension on the quads and glutes, move smoothly in and out of this extended range of motion, and you’ll see how demanding this is on the legs and the lungs. – Dr. John Rusin

Normally lifters will set up on a standard bench. But body size, body type, and leg length, and anthropometry are not standard, so it make little sense for everybody to use the same height bench. Using a bar is a simple fix because you can make to customize the height of the back leg and get a full range of motion with a perfectly neutral spine. For the average lifter, this height will be somewhere between 12-16 inches. – Dr. John Rusin