I almost always vape my bottles to empty but I've been doing it for a very long time, relatively speaking of course. I agree that after about 1/2 you'll need to adjust your squonking a bit. It will come with practice. My favorite size REO changes from day to day depending on my activities. Past month I have made the mistake of leaving the house with near empty 3ml bottles and, on both occasions, picked up a throw away at a fast stop store. This is less likely to happen with the 6ml bottle in Grand and VV AND a bit more organization in ones life. Must be something in the air..... last month DH left the house once with "empty" and another time he left all vaping gear at home.
Good for you doing your research. Welcome to REOville.
Feisty Alice