IT IS VERY DETAILED.
but in my hearing, i often hear they are pronunced the same syllable, (stopping plosion 't' can be ignored ),i hear the same syllable and different tones.
i remember when i was little ,we studied british kind of english, i remeber 'can' and 'can't' is different in vowels.
and now i know that American speak the same vowels.
and i still think that all of u just using a "stressly go down " tonation in "can't" and a "smooth" tonation in "can"
"stressly go down ""smooth" is just my saying, i m sorring that i dont know the correct term