I'm in agreement with Absintheur, I only use single coil cartomizers, too. I also think his theory is sound that the top coil coil can burn the material that surrounds it if the batting can not keep it moist. Look at these photos of a dissected dual coil cartomizer (click to enlarge them).
View attachment 172466View attachment 172467View attachment 172468View attachment 172469
One could possibly use a drill press to punch cartos, but who has such an expensive machine to make holes in a carto? I've been perfectly happy getting one or two laser-drilled cartos from vendors, they wick juice fine. I've only needed to punch larger holes for one juice, and that was Boba's Bounty, a very thick as molassis 100% vg juice.
Smoktech made the original DCT (dual coil tank) and marketed their new at the time dual coil cartos with them. The name stuck for all tanks made by other manufacturers. Of course you can put a single coil in a "dual coil tank".
I assume the carto manufacturers are reluctant to put their laser-drilled holes higher on the carto for fear that it would upset the inner tank pressure once juice levels get below the top hole, and therefore you'd be sucking on the air in the tank, instead of the juice. It must not work that way in real life, because that seems to be the way fourthrok punches hers and she is claiming great success with her method.
It all boils down to finding a system that works for you.