I feel like I'm in-between sizes or something. The medium Apple eartips are more comfortable but tend to sit farther out of my ear canal and feel like they're working their way out. The small eartips stay in more securely, but sit uncomfortably far into my ear canal and lose seal when talking or putting my head in certain positions. I eventually settled on the mediums and have become accustomed to the feeling of them "falling out" even when they're not.

But yes, odd to hear that other people also have issues with the left ear fit, because they must be identical shapes. I wonder if human physiology averages to the left ear being smaller or something. Although I feel like the right ear falls out more easily if I switch to the small tips...