besides, modes are very specific collections of notes.
the C Ionian Mode is JUST the noted CDEFGABC. if i
play a piece on a C harmonica that also includes Bb,
and Eb, but is still in the key of C, then i'm still
in 1st position but no longer in the Ionian mode.
another (common) example is the G blues scale: if i
play G blues on a C harmonica, it's second position
but i'm not playing in a mode.
but again, that's ONLY if you all you ever play is
music in certain modes. there's got to be hundreds of
other scales beyond the 7 modes of the diatonic scale.
in fact, the vast vast majority of modern music around
the world isn't limited to those 7 modes. to try and
lock modes and positions together is to artificially
limit yourself (unless of course you only plan to play
modal music, in which case i suppose it makes little
difference).