Thanks but what is the cause?
I'm not exactly sure there is One Single cause of Spit Back? It could be that Multiple things can cause it. Or that Multiple things need to a occur for it to happen.
For me, too Loose or a Very Fluffy wick can sometimes cause Spit Back.
If you are getting Spit Back, try something Different with your wicking technique. More Cotton. Less Cotton. Rolling the wick. Not Rolling the wick. etc.
Also, sometimes moving the Coil slightly in relationship to how the Airflow hits it can make a Difference.