The dual coil deck certainly works, a bit too well! Lol. A couple of days with it and my 3mg juices = nic overload! 
After reading
@Heartsdelight advice of trying a clapton coil in the single coil deck as a possible solution to my wicking issue, I thought what the heck, why not.
Now, when swapping out the dual coil deck for the single, I realised that when I previously swapped out all the black o rings (thinking the problem was a vacuum issue) there was one I had not changed - the one located on the bottom of the deck. I had overlooked this one because I had left the deck screwed in. So, I decided to change it. And hey presto!! Single coil clouds bro! 
No more anaemic hits after just a couple of hits. I'm now seeing good bubbles without having to open up the top fill. Ie it's wicking good now.
Seems like the problem actually was a vacuum issue. Something like a situation where rather than the tank's vacuum sucking in juice into the wicks, a leak (due to the bad o ring) would instead allow air to be sucked in??
Strange though cos the 'bad' o ring doesn't look bad at least to my naked eye. Maybe a tolerance issue with its size or something.
You can see in the pic below the culprit o ring along with me pointing to where it's located on the dual deck (same thing applies to the single coil deck):
View attachment 629745
@pappasmurfsharem I suggest u try changing all ur o rings.