Here's a simple trick for understanding CBMP. Stand with one foot in front of the other, a comfortable distance apart.
Drop the back knee to the floor. If it lands inside the front heel you were not in CBMP. If it crosses and lands outside the front heel, then you were.
This stresses that CBMP is a body position, not an action. One (but by no means the only) way to arrive in it is to take a step with CBM.