The axiom is a small deck & does have small wicking holes compared to the factory made coil that came with it.
I think larger diameter coils have their merit, I think having less 'dead space' inside the atomizer in theory would give better flavor. I think the problem is attempting to predict what the (incoming and outgoing) air is going to do in any given setup, we don't really have any way of knowing. The coil and wick work hand in hand so in something like an RDA you have quite a bit more leeway, where in an RTA/RDTA (or genesis) the more efficient wicking setup would probably dictate coil diameter size over space available.
I think once you have built a few coils you'll find that actually trying coils is easier (and less time consuming) than trying to predict what will happen.
We are pretty much in the same place, I am 3 weeks smoke free, and I also did a ridiculous amount of research before diving in. Only thing different is I went RDTA (genesis).
I quickly switched to SS316l in TC mode, and will probably not go back. I'm running simple single-stranded 26g spaced 3mm 8 wrap coils in dual on a Limitless RDTA+ (45w 420 degrees DTL). I tried 28g but could not get the screws to connect with it to my satisfaction, I may try and twist it next time, or try parallel contact.