Had the same problem as well, especially on levels like Hot and Heavy. Levels that have narrow areas seemed to have the issues like that for me.
It was definitely improved in HM2, but there is one level in the game where the hit detection goes wrong. On the prison escape level, those people that charge at you always (at least when I played) seem to hit me way earlier than they should have. Sometimes they even cut corners, if you are hiding behind one to kill you.