I wouldn't try and do singles on the tobh. Make a horizontal coil that is around 2 ohms, check it several times, then do the same again. You then have a dual coil setup.
For what it's worth, the tobh seems to run best, for me, at around 4 ohms. Much lower and unmodified airflow becomes an issue,
Assume you will have to try it many, many times till you get something you like.