I typically only do it for a split second before I take a drag. In playing around with it, I found that even a long pre-heat only produces a small amount of vapor. Which makes me think that it may be harmful, or increase the residue, to cook the atty with no airflow to clear the created vapor.
Your mileage may vary, try it:
Hold the button for one second, two, four or more seconds. Release the button. Then take a drag. Observe the vapor.
I think this is the reason you've only gotten small amount of vapor with the preheating...
You're not supposed to release the button then drag....
it's just a matter of pressing the button for a moment then start dragging
while still holding the button.
The idea is that atomizers take a while (relatively speaking, a second or so) to get up to the optimum temperature to vaporize the liquid.
So you let it warm up a second, then start dragging.
THis is one of the biggest reasons many people dislike automatic batteries.
You have to take "Primer" puffs to warm up the atty.
Personally, I don't really do this anyway...
I'm dragging instantaneously at the same time I push the button..works just fine for me.