>>294939465
The IK is trying to keep your feet on the ground and the toes are the furthest point down from the hips. If you raise yourself above the avatar's height, it'll go on its tip toes to correct for it.
Also when you look down, it brings the body upwards because of the IK's math on where your body is relative to the headset which causes it to tip toe too. You cannot fix this without playspace moving down a little bit (and eternally squat) or by getting full body tracking.