Too much flavouring perhaps....
May I suggest upping the ratio to 70/30 or 75/25 ???
Not being funny my black Vapefly Galaxies RTA started leaking like a sieve
re-wick, recoil, rewick, rewick long short tight loose cotton blah blah blah...
Still leaked ???
I mixed up my own 60/40 instead of 50/50 which helped quite a bit
but still a slight little bit of weeping through the air intake port
I then changed the block by rotating the two hole block 90 degrees to a single port
(yup you got two blocks with 2 holes & single hole & a slot & slightly larger hole)
So you have two cubes on the Galaxies RTA with 2 options making 4 in total
Viola - no more leaking, though to be honest I might have been able to just resit the two hole block
(may have come loose or never fitted 101% in the ultra high precision Chinese assembly line sweat shop)
But anyway the thicker juice helped and more so reseating or different air block
Now you do not have the option to change airblock like on the Vapefly RTA so are stuck with one under coil
So all you can do is alter the viscosity as well as coil/wicking methods
The thinner the viscosity the runnier the juice is and have a possibility of seeping into air passage
once it begins to seep you are likely screwed as more juice will at least try to follow blah blah blah
(well like flooding/leaking you can try to blow the crap out & up the watts but if bad it'll continue to weep)
So it is fair to assume on "some" instances a larger hole will seep more on lower viscosity liquids
Why has all this crap started - Fuctifino
Maybe central heating, warmer homes, maybe old juice, variations in viscosity etc....
But if you have exhausted all options on coil/wicking then it is possible the viscosity may have altered slightly
Strip everything down, flush it all out & dry
then try a 70/30 or 75/25 ejuice is perhaps next port of call
RTA's and the size of air intake on decks vary a LOT
(been glancing at numerous MTL decks lately - sad thing I am)
Which has lead me to believe them decks/tanks really vary a lot
Probably why some tanks leak more than others through air intakes on certain juices
(and why others do not suffer quite so much on 50/50 juice)
Pen stick stuff & say stock coil tanks can run on almost anything from 70 PG to 70 VG
Often a 50/50 mix works great on stock coil tanks - but not so great on RTA's perhaps
(especially if you got a rather large air hole under a low sitting coil)
Now you might have the coil sitting ultra low, just a whisper above the air hole
which is tapered, now if the juice builds up and just slightly soaks around the coil
it might just start to saturate enough the juice just touches the nozzle
(especially when air flow stops after you finish the draw)
DROP - and off you go with juices seeping down the air inlet
(1mm might be a bit low - try say 2mm perhaps)
So try raising the coil up a little bit maybe to avoid saturation reaching the air nozzle easily
(might help but also a thicker juice too, so raise the coil and if no joy increase VG ratio)
As for dry hits - I'm guessing the wicking or thickness of cotton
This is still the guesswork bit for everyone
I wish you could take an easy peasy formula for wicking but it isn't quite so simple
If all cotton was exact thickness & type and all juices exactly the same
then it might be possible to assume the inner diameter of coil say x 3 or something
(stripping off top/bottom layers blah blah blah & arrive a rough ball park cotton width)
EG: 2.5mm ID coil x 3 = 7.5mm width to cut, strip off layers twist/roll wick
or
EG: 3mm ID coil x 3 = 9mm width to cut, strip.....
Alas cotton, coil, juices, tanks and crap are not equal and this figure of 3 x coil ID is not set in stone
(never can be as explained as too many variables)
However it might give some an idea of x2.5, x3 or x3.5 etc... something to work with
if you eventually find something that does work for a particular tank/setup
(don't flame me, but found about 7.5mm strip works OK for last couple wicks on a 2.5 coil just recently)
Now doubt this will work a few times then go crap just when you think you sussed something
Not saying wicking doesn't play a big part - but viscosity is maybe the next thing to examine/consider maybe ???
(well from what I have also recently discovered myself)
just my 2 cents - best of luck