Hi Simon,
Popping, to me, seems to be a combination of how much wick you have in the coil, and maybe a little more importantly, how close the coil is to the air inlet. So its really a balancing acts between these two variables. You should get the coils fairly close to the inlet, this cools them down, and just the right amount of wick helps keep them cool while they are saturated, and this does a good job of containing popping somewhat, depending on what your coil is running. Once you get below .2 or so, you will have popping regardless. I tend to like the popping quit a bit, so I run a little more wick through the coil, but since its Muji cotton, it does`nt suffer if a little extra is put in there.
It`ll take some time for you to figure all of this out, but it really is a personal learning curve you have to go through. You can get allot of tips and such here, but in the end, you have to get an idea of what works for you, as there are a gazillion ways to coil and wick a good vape.
BOL.