Carto tanks work based on a balance between capillary action, surface tension, and a vacuum lock.
The air should only be able to get into tank through the same hole that the
juice is trying
to get out of. This causes a slight vacuum and is what keeps the juice from just draining
out through the holes in carto.
If you have a carto with an "airy" draw or your drip tip is loose enough to allow air in, then
you might not get enough suction to overcome the slight vacuum in the tank. Conversely,
if you have a carto with a "tight" draw, you may pull too much juice and get more flooding.
There are so many variables, some experimenting will be necessary. Even your environment
can effect how well the tank works. My set up is a Smoktech single coil carto pre-punched
with 2 or 3 holes ( I use a sharp point to make them a little larger ) and 70/30 PG/VG juice.
A full tank works well, but I have to start using primer puffs when I get to a half tank to keep
carto moist. I live at sea level with high temps and usually a high barometric pressure, if I was
to live at a higher altitude with cooler temps and lower barometric pressures, my set up
probably wouldn't work as well.
Another thing to consider is, just as you sometimes get dud cartos, sometimes you get a carto
that just floods more.