In general, a large speaker's drivers occupy more linear space than a small speaker's drivers. For example, the distance between the topmost driver and the bottom-most driver is larger on the M80 than the M22.

As a rule of thumb, try to put a proportionate amount of space -- I'm not aware of an exact ratio, so just experiment -- between your ears and the speaker in order to allow the soundwaves coming from each driver to reach your ear coherently.