Recommended Tray Icon Size and Format

I’ve built a snap that displays a tray icon, but I’m having trouble with sizing the icon.

Originally I was using an SVG set at 20px:
<svg xmlns="http://www.w3.org/2000/svg" xml:space="preserve" height="20px" width="20px" version="1.1">

That worked wonderfully for Ubuntu and Fedora, but in Manjaro the icon wound up repeating itself in the tray display. Manjaro apparently wants an icon set at 22px. When I set the SVG to be 22px, it was great in Manjaro, but then in Ubuntu it looked as though it was tiny – like 5px or something.

I tried making it 100% instead:
<svg xmlns="http://www.w3.org/2000/svg" xml:space="preserve" version="1.1" viewBox="0 0 100 100">

This just made it tiny again in Ubuntu. I don’t have much experience with SVGs, so if there is a good way to make it the right size across distros, please elaborate for me!

I also tried an ICO with versions at both 20px and also 22px. This again worked well in Ubuntu, but in Manjaro it still repeated itself.

What kind of file do the rest of you use, and what size do you make it?

Thanks!