going half way in a squat does not constitute bad form. bad form would be to break the arch in your lower back, or to let your legs buckle, or to have a different motion using heavy weight rather then with light weight. obviously when going near failure your form will break a little but this should not be occuring with lower intensities. Is it bad to do board presses to improve your bench press and to hit the triceps hard even though it makes the bar move half the distance? i don't think so considering every powerlifting routine includes them.
are we talking about parallel powerlifting squats (wide stance) compared to oly fulls squats (close stance)? there will be a difference in these numbers but if you are talking about the same stance position as far as your numbers go if you can squat half way 405 i think you should be able to full squat way more then 225. try using adjustable box squats to get lower. laters pk