Don't do what I do, or did.Yep. No rules.
I tried a bunch of different places mounted, and then decided to just plop it on the floor tom head.
As I get older, the positioning of things become permanently temporary.
My cowbell is mounted directly onto the hi hat rod, above the clutch.
I use it a lot, and usually in the same way as I use the hats, so it made sense to me to have it there.
E.g., my band plays Love Shack, which has a cowbell on 1 - 3 -1 -and- 3, and I just switch between hats and cowbell for those hits.