Comment by dhon_

This is the best explanation I've found of the mechanics of pitch bending https://youtu.be/Fp-GxEaChr0?si=-E9uDTQx51gtnd9C

Essentially, match the size of the resonance chamber in your mouth to the note you're trying to bend to. This is different for every note you bend. You can find the right size by making "hissing" noises while breathing in (without harmonica) and matching the pitch.