I think you are a perfect example of someone who would benefit greatly from the ASA DVD, so find a UIC or someone in your area who has it and watch it or purchase it yourself. Watch it over and over. I took some screen shots of the DVD - PU Stance section and was going to post them but I think I might ruffle some feathers by doing that.
So I just dug around in my pics until I found a decent shot of an umpire (not me) - I'm sure this ump could be critiqued but I think its good and certainly good enough for training
Red Line: Good heel toe - hook the catcher. Your back foot should be back and your forward foot should be set wide enough for you to have your eyes at the top of the zone forward to a direct line should run from the forward foot heel to the reat foot toe. The forward foot on a righty is the left, on a lefty, it is the right foot.
You can lean a little but bend at the knees. Be comfortable.. this is where mom, god and mcdonalds comes in.
Blue Line -- ASA uses different terms but generally, aim your belt buckle at the the right outside corner prior to going set (you will straighten as you set).
Now you should be able to see the entire zone. If you cant, adjust your hook slightly around the catcher but keep the same alightment.
Green line - Track. Forget the old school baseball thing about not moving your head. Slightly move your head, keeping your nose on the ball tracking the ball all the way through the zone watching it into the catchers mitt. See the whole pitch from release to catch. No need for an exaggerated head movement., but a slight tilt so you can track it.
I think if you master those beginning elements you will improve your zone and set a foundation for tweeking it.
Sometimes you find your zone and.. its not received well. It must be believable and if game after game you are getting problems, you may need to reevaluate the pitches you are calling and your zone.
Hope this helps!