I use SS316L, 28 gauge, 2.5 mm ID, 7 or 8 wraps, slightly spaced, on my SXK clone. I squonk in TC only, but it can be run in VW (power) mode too.
The air holes all point toward a central point, so you don’t want too long a coil, IMO. I usually run it with all three holes open, only occasionally with one or two holes.