BTW... there is a
Tips and Tricks thread that has a lot of useful, "stickied" information.
Since there are some recent fluff discussions I'd like to add some personal observations.
I, too, started my Spheroid and Heron builds with the help of the Internet (and this forum as well). I think starting with (fluff v2) dimensions of 20mm x 40mm for the Spheroid and 17mm x 60mm for the Heron makes for a pretty good base point. Now, I primarily use 50/50 eliquids and those starting dimensions work great with any wick I've used; the fluff isn't too tightly packed as to reduce capacity and it isn't too loose to not hold onto the eliquid and flood the atty.
However, we all know that all liquids aren't the same and I recently got a taste (pun intended) of that recently when all of a sudden my Heron would flood even though I used the same eliquid, and build, for months before.
Unfortunately, it took me awhile to track it down to the fact that my eliquid was thinner - due to added flavor shots which were, presumably, PG-based. An extra 10mm of fluff in the Heron tank and, voila, fixed!
...
Thinner liquids (more PG) need more fluff and more viscous liquids need less fluff. A good general rule of thumb, for me, is to adjust fluff length in 5mm increments for the Spheroid and 10mm increments for the Heron. I use 20mm x 35mm (Spheroid) and 17mm x 50mm (Heron) for thicker (max vg) liquids and 20mm x 45mm (Spheroid) and 17mm x 70mm (Heron) for my thinner liquids ... like the 50/50 liquids that have extra flavor "shots" that I'm guessing to be PG-based.
I'm sure I could tweak it by a few millimeters, each way for each juice, but this generally seems to hold for me.