So, a more serious response to the question at hand... The amount of oxygen in the jar will affect the aging either good or bad, depending on your preferences. If you are worried about oxidation effects and/or aerobic fermentation, then reduce the empty space in the jar by packing the tobacco tight in there and/or use a vacuum sealer attachment for jars to remove more of the air. I can't speak to whether more or less air is better as I haven't done a side by side comparison of that, but I have not yet been unhappy with my cellared tobacco regardless of air space in the jar.
Also understand that at some point any amount of the oxygen in the jar will have likely been consumed. I do not know the necessary equations to determine the time frame for that as there are several variables involved, including temperature, volume, bacterias and sugars present, etc. Aging beer is a very similar concept to aging tobacco in many ways.
