Curious, my bell tent has superb venting from the bottom to the top? Indeed most seem to have several adjustable "windows" with mesh in the side walls and vents in the apex?Fires in tents of any sort are always a danger. Used to have a tipi and even with an open fire because of the flaps at the top it was much safer. Plenty of ventilation for the fumes to escape.
Sewn in or zip in groundsheets are also a bit of a problem as there is no airflow from the bottom to the top. I don't have a fixed groundsheet if I have any sort of heating and leave a good crossflow of air either from door to wall window flap or window flap to window flap.
It's very tempting to button up tight to keep the warm air inside, but you also keep any fumes inside too! Fire needs to be out before sleeping and some venting too while you sleep as fumes from the fire can still be around even if you think the fire is out.
Yes the chimney needs to be higher than the tent to carry smoke and fumes above the tent and away.
I've camped in tentipis with a fire both open and contained in a stove. They have excellent venting that can be controlled from a sleeping position. You don't have that with a bell tent. That makes them more dangerous.
I'm surprised they are so popular with less experienced " glampers " nowadays.
Careful management is important . Many glampers come from a sealed centrally heated home and try the same with bell tents. I'm surprised there havnt been serious accidents.