The technique day is a good idea, but it's important to remember that your technique with the bar has almost no influence on your 1RM technique. Your brain literally thinks it's a different lift. There's a couple of things you could try to fix your technique (if you think it's really that bad):
1) Do your technique work on DE day. Don't do box squats, do regular squats with good form for the standard Westside set/rep protocols. (probably what I would recommend last)
2) On ME day do regular squats for three weeks (you don't have that much time until max day anyway) and do this:
week 1: 85% for 10-15 sets of 1
week 2: 90% for 10-15 sets of 1
week 3: 90%+ for 10-15 sets of 1 or standard ME
All with 1.5-2min rest.
This option would be very good because you'll practice moving heavy weights while you're fresh (technique with near max weights). Obviously lower the percents if you think your max has decreased.
3) On an off day do this:
week 1: 85% for 15 sets of 1
week 2: 87.5% for 15 sets of 1
week 3: 90% for 15 sets of 1
All with 2 minutes rest. This shouldn't be that challenging because of the long rest interval, but it should improve your form for your max day.
If you decide to do option 3 you might want to back off on one of your assistance exercises the workout before. Also, remember that Louie emphasises technique too, despite all the talk about assistance exercises. The point is, the assistance lifts are there to facilitate technique development as well, so choose them appropriately.