Problem solved. Replaced the base with one with longer threads. I am no longer running the protank on my
mod anymore though.
I have a zip lock full of Kanger heads awaiting re-coil time. I never noticed that there are dimensional differences in the heads. When I tried to use a Protank head in my Evod, the threads wouldn't catch because the height of the threaded portion was held away by a longer overall height between the threads and the air tube. You are right. If you are able to install the wrong head, performance can suffer and I can see how gurgling and dry or wet hits could occur.
The right head is a must for a good vape. Kanger is reported to be replacing all heads with a universal design. I think that design is the same as the one for the T3S. It has the longer air tube and works in the Protank, the Evod, the T3, and the T3S.