I just noticed the same thing, I didn't exactly fill the cap, and filled the premium cartomizer from the battery end. It's a measured 0.5 ml exactly, I just measured the amount.
What I would like to point out now is that this is Wowliquid, and I'm seeing the best
ecig performance that I have ever seen. Because of this, that this is Wowliquid, I am also seeing more clouds per second, so it's
hopefully not getting used up as quickly as the premium nobacco liquid used to. We'll see. It may be that even with less juice, the carto with 0.5ml Wow can last just as long as it used to with the original liquid
--edit add: Then again, it could be that it's also using up more liquid per second. Whatever the case may be, it's wonderful--Premium cartos with Wow liquid.
Also, 0.5 ml is the amount I used, it can hold more, but I just didn't try to put the maximum amount in it.