Spinfit was certainly on my radar. I'm assuming that these are the right size for the earphones. But how do I know they are the right size for my ears? How do I know I should go with the medium rather than the large?

Ok. I have my Beyerdynamic Soul Byrds. I'm pretty happy with the sound, EXCEPT for issues with pads. My right ear is pretty good. But my left ear is not connecting well enough. It's getting poorer bass response and less isolation. I have to boost the sound on that side to make sound balance. I...