Lotus position right knee floating?

This isn't a Buddhist question per se, maybe better placed in a yoga or Taoist thread but anywhere here I go: When I am in the lotus position (classic right leg over left leg as instructed in all Buddhist guides) for the past 10 years, my right knee has always floated a quarter of an inch off the ground, even if I try to adjust my position by sitting offset on my mat. Anatomically speaking, I don't see how anyone can have both of their knees on the floor.. Although I feel energetically blissful whilst maintaining the posture, the posture feels uneven, imbalances my torso, and I feel uneven pressure on my right thigh and must end my lotus posture in about 10 to 20 minutes due to the pressure on my right thigh... Sometimes I switch reverse full lotus and that makes me feel more balanced. Am I doing something wrong or is this something all advanced lotus meditators must deal with? How can I remedy, deal with, compensate (et cetera) my lotus posture? Also, this is a separate question but are there any passages in the canon that speak about posture? Any suggestions in any realm, physical, environmental, or even mental are welcome.