It's not something that is set in stone. One persons 3mm dia, 0.5ohm coil will sing for them. Somebody else can use the exact same coil in the same attie & it's shit to them. Airflow, wire type, wicking, juice flow, chamber size, length of drip tip, position of coil all affect final result.
Don't analyse, just build a range of coils at different diameters/ohm & test. Make a note of what works for you & go from there.
I've been building coils for nearly 3 years but I still tinker even though I have builds that work fine. All part of the fun & learning process. Vaping isn't learnt from a text book.