like dice pointed out, the lower the resistance the bigger the airflow needs to be.
And vice versa, a higher resistance needs a smaller airhole for optimum flavor.
Take for example the reomizer. Stock it has standard a fairly small airhole (3/64" ).
It is a true flavour-wonder with microcoils 1.3 to 1.5 ohms, also really good
at higher resistances.
And it is for mouth-to-lung inhales... very satisfying.
My trident has 2mm airholes (i guess... idk for sure). And my sweetspot flavorwise with
that is at about 0.6 ohms on a mech.
This is for lunginhales, so the vaping and flavour-experience is different.
As for the coils: Why not just duplicate what you liked in the protank on your RDA?
2 of those microcoils would be around 0.65 ohms, which should fit your airholes fine.
Keep the coils close to the airholes, and try a standard cotton wick pulled through
the coil... less is more. If that tastes right, you can always experiment with some
more fancy stuff later.