i would be fine with a 22mm, but a 23mm would not be unwelcome. It would mean that the tube stock, assuming mac isn't wasting 99% of ti/al by reaming it out, would be 0.5mm thicker. I personally would love thicker walls, especially in ti.
i've have to go caliper my other atomizers to see if any of the skinnier ones fall in the 19-21mm diameters, but all my high-end stuff is 22+
Guys I will never really go into "production" I have always tailored toward "Custom" If you want a 21-22-23-25mm mod I can build you one