I think that's the whole issue here, that you and I think most in the US pronounce most or all of them the same, whereas I pronounce
John and
Jon with a very short vowel, and 'Jahn' with a long O, ironically as though I was saying
John in an american accent. I would pronounce Jawn the same way I pronounce Lawn, which is again different from Jahn and
John! oh dear!