I don't even know where to start....
Please get rid of the smith machine squats, and don't put plates under your feet. You just need to learn how to squat, and not find ways to get around it. There are alot of tall power lifters out there that squat just fine.
First, go read the "squat" sticky on the powerlifting board. 2nd, try box squatting to learn proper form. Get a wide stance, press your knees out, and sit back. It looks like this:
365 Squat
Goodmorning the bar out of the rack. Walk the bar back, or start using a monolift (if it's available to you). Before you even lift the bar out, the traps should be squeezed together, pull the bar down on you like you're going to break it over your back. Get a nice wide stance, and a tight arch. Don't start with your knees hard locked. Don't bend your legs...just right there in between. Try to keep the bar moving in a straight line up and down, and preferably over your hips. Then, just sit back. This is REALLY a back and forth movement, not up and down. The stronger your posterior chain, the more you will squat. Use your hamstrings to lower yourself (tip from Bob Youngs). Concentrate on keeping your knees out wide/pressing them apart. To ascend, drive your neck into the bar (looking forward, not up) and flex your glutes/hams to stand up. Spread the floor apart with your feet the whole time. Feet should stay flat, knees over
ankles and out wide, bar over the hips.