Have never tried the experiment, are you saying it won't light at all? Or simply that it won't remain lit? In either case, I would agree that lack of oxygen is the problem. In the latter case, wax smothers the flame. In the former, perhaps the body of the candle is blocking the upward flow of air away from the flame, preventing fresh air from flowing in.
but... since in space where there is microgravity, the flame goes in all directions. I'm going to try the upsidedown candle experiment and report to you the results... if I get around to it
Have you tried the candle oscillator (see diagram, below)? Start with a needle thrust through the candle's center, perpendicular to the candle and with ends resting on fulcra. Burn the candle at both its ends, and watch it see-saw. Would its period be approximately linear or nonlinear?