A major contributor to tongue bite or hot smoking is a shallow transition from the draft drilling  at the button end of the stem.  This causes the smoke to remain in a narrow cylindrical column as it exits the stem into your mouth.  There's not enough room for the moving column of smoke to spread out and slow down before it exits the stem.  The first drawing below shows a common condition.  The second drawing shows our remedy.  Lengthening the taper, or putting one in where one didn't exist, will allow a smoother airflow transition.

The problem -- no space for the draft air to expand

Remedy -- lengthen and smooth the taper from the draft drilling