@ Steven, think of the force vectors as knee extension and hip extension.
I dont think with the way YOU squat low bar, you would notice a difference in vert training. Very minimal at best since youre already so upright. I have seen it happen that, someone switches to a more knee driven squatting style, and gets a much higher correlation to vertical jump, olympic lifts, and 10yd sprints.
What I can say from seeing this every day, is that if I see a guy squatting deep and upright, a very high squat relative to his bodyweight, I can put the bank on it that he will jump well in the standing vert, start well in the 40, and if hes not already good at the olympic lifts I can get him there easily.
I can NOT make this statement with guys coming in who have been low bar squatting, and have a high squat #, but not nearly in the same manner. If you test the front squat, many times these guys will have much less success there, and the first group I referenced will be much closer to their squat. The only thing withstanding that they are able to hold the rack position, and this is easy to teach and get around.
The bottom line is that a heavy squat done deep and upright means that the LEGS are strong. If the LEGS are strong, the athlete will nearly always jump well. If the low back is strong, this doesnt mean the same thing. This is also why its hard to correlate vj with the deadlift.