just wanted to interject in here...

A2G is the GOAL.

however, do NOT force it. If your lower back rounds as you go down, then you probably have a weak posterior chain and abs, as well as tight hammies

do NOT hit A2G until you can do it WITHOUT rounding the back. Just keep going down as low as you can "comfortably" (hahhaa,...comfortable squats) go, and NO rounding of the back.