I've been training with Box Squats for the past 3 weeks and my strength has increased tremendously. For the past 3 years, I've trained with the Manta Ray which forces your back to be more erect than without it. I've been alternating back squats (Manta Ray) with front squats (Sting Ray). On Box days, I go 1" above to load up more weight followed by parallel and below parallel. Funny thing is, I tried the Box Squat w/o the aid of the Manta Ray and I found it to be a whole lot easier!! I will still use the rays to build up more strength since they make squats harder in general due to even weight distribution throughout the body. I have recently added on Zercher Squats. These Zercher movements kill.