Which is why it’s a good idea for those who order glasses online to still visit an optician for a fitting/adjustment. Everyone’s ears are different and not all frames are going to fit the same way. Millimeters make a huge difference when at the scale of your eyeball, and there are tools and techniques that optician can use with your lenses and frames that could improve your quality of vision (usually for free, in my experience.)

Edit: I meant optician, whoops