are you training for a powerlifting meet? if not then quit doing back squats. i quit a long time ago, my legs have grown. front squats are my main lift for legs now, you will naturally sit back and go deeper in the hole. it also puts more strain on the abdomen instead of the back. also bulgarian squats. lets say your 1rm for back squats is 300. you'd think that for bulgarian squats your 1rm would be 150. wrong. take 50% of your 1rm for back squats and do bulgarian squats, i guarantee you rep it out for 5+ reps. your postrior chain is the weak link in back squats, you are not effectively hitting your legs with back squats. so if you are doing squats for leg development, stop. switch to front squats and bulgarian squats and see what happens. also for the posterior chain i recommend glute ham raises, good mornings and hip thrusts.