Well, the information out there has been a bit sketchy regard my research into it, but I'd have assumed that since the power from the battery is divided between two 1.8 coils, that the coils would take longer to heat up or not heat up as much as a single-coil 1.8. I'd have guessed the ultimate "resistance" (though I'm not sure this could be measured) is somewhere above 2.5. Testing seems to point to this direction because at 3.3, this device really doesn't give more vapor than I'd expect from two 3.0 heads running at the same time. I'm sure that number isn't accurate, as 1.8 coils will probably heat up faster no matter what, but it's simply something I've questioned and not really found a big answer to.
And to others, I'm sorry that others out have a divided opinion on "user error", but I believe this is a very elitist view, especially when such users rarely offer an explanation on their own methods and what they are doing to get the best results. If there's a disagreement, simply offering advice on techniques always benefits everyone.
The aspire tank is a system that is built to load and go. The heads were not made to be rebuilt and thus the company didn't intend for users to take apart the heads, prime them, and all that good tosh, and then put them in. I'm sure someone out there is dropping a few drops into the head before they install it, but I didn't do that because without precision, the juice could go right to the bottom of the head. Other than that, I let my tank sit there and wick for 15-30 minutes, doing stout primer puffs every 5 minutes or so. Then I vaped at 3.3 and did a few tests at 3.8 to see if I could increase the flavor and get rid of the god awful yeasty taste - a bit like fish oil, it was. I also used two types of air controllers, an official one, and then a beauty ring where I taped one hole up. Neither made any real taste or wicking difference.
My personal belief is that there are a lot of heads out there right now for this system that the factory has labeled "rejects", but that they have sold them to vendors anyway; a prime example of this is the 4-hole system that is floating around. Or they could be clones. Even the vendor that I bought this from could have felt pressured to buy clones or rejects after the initial stock of heads sold out. No other explanation. I've also been in contact with reviewers who have also experienced entire packs of "bad heads" and that the system suddenly started working right with a new pack. At $13 a pack, I don't support that type of quality control in the vaping industry and won't be experimenting with a new pack unless a vendor wants to send me one.