I would check a few things:
1. take of the PT's base and remove the head. On the very bottom you have the pin that makes contact with your device; just below that is a rubber/silicone grommet. Sometimes that bottom pin can get pushed in compressing the grommet making is bulge past the edge of the pin which restricts airflow. Try pushing the bottom pin in a bit compressing and bulging the grommet, then trim with an exacto/razor anything protruding "over the edge" Once trimmed, pull the end pin back out just a bit, being careful to not pull it all the way out. Screw the head back in to the base and check airflow.
2. If airflow is still tight, remove the base again, leaving the head in place. Look at the base where it has the 510 connection and notice the air holes just above the threads, as well as the groove that is "notched" in the bottom pin that contacts your Vamo. Align that groove in the very bottom with the air holes on the side, by twisting it carefully w/ your fingernail or a small flathead screwdriver. This should help direct a bit more airflow through the ProTank.
3. Inspect the wicks by removing the "post" from the head (leave the head in the base, and hold the base in one hand then grab the post (the part that inserts into the tank) and rock it back and forth until it pops off). Sometimes the wicks can move around. If they are not running across the center, directly over the coil, that can also restrict airflow. Just make sure that either side of the coil, where air has to pass, is not being blocked by anything.
This got me from no airflow to much better airflow, though it was still just a little tight for my liking. So after these steps I took a very small "needle" tipped file (round base to very small pointy tip) and filed just a bit to open the air holes in the side of the base a little more. Now it draws perfectly, no extra base needed.
-Best of Luck-
