In the V.Waltz, as in all other swing dances, one never bends the knee as a direct action. A bent knee is a reaction to the "compression" used to power the movement, which in turn is reaction to how you want to move your body thru the music.
One can use a good deal of compression , resulting in a fair amount of "lowering" but it will never look obvious if produced with the right dancing intent.
One can never measure the quality of the movement based on how much the knee has bent. If you compressed strongly, you will produce a longer length of stride and it follows that you will collect on a softer knee. One then has the power to produce a smooth and unaffected rise.
One often see couples trying deliberately to either bend or not bend their knees as a primary intent. The ones who try not to bend their knees end up with a stiffer movement without much flight. One can never get the combination of power, balance, continuity, length of stride, etc. from this idea. The ones who deliberately bend their knees get low and sitting back. They cannot produce the effortless power to produce the flight and rise so they pop-up creating a very obivous rise-n-fall which becomes the dominant characteristic of whatever swing dance they are doing.
Leave the bending of your knees to that which best, your body and the unthinking mind. It either knows or will figure out what it has to do if you leave it alone.
