There could be two things going on:
1. They are easier to take longer hits from and so you are burning more juice without realizing it as Crispy said.
2. your juice is thin. Granted a higher voltage might burn the liquid at a higher rate due to the increased heat, but that would just be minimal, as the base elements of your liquid would still have to go somewhere (vapor) and it is the water that would evaporate faster with increased heat.
In reality the heavier vapor requires more juice, which is the way I like it personally. Mixing your own makes it very cheap and you get exactly what you want, tailored to your particular cart selection. I use the ce-2 rev 5 XL (1.8ml) a lot. I make a 93-95%VG juice that vapes perfectly fine and with huge vapor clouds. Clean them once every two weeks, and I have had some last for over 6 months before putting them out to pasture and starting new ones. the old ones work, but wanted to start fresh and use the wicks for rebuilding my ego-t atty. I usually have about 5 in rotation. Just cut the openings into a V on the side of the stopper that sits on the cup that seals it to open up the flow.
Theoretically, unless you account for an open bottle "drying out" by the water evaporating, the only thing that can happen to liquid is that is burns. Unless you have a heavy buildup in a very short period of time (and that would still be a minimum amount of liquid), then you are sucking in all that liquid as vapor.
Better that than a dry hit.