I bought 20 from the earliest runs and have acquired a few from later runs. From the bulk buy(s), 10 center black stamps and 10 bottom right rainbow stamp and marked like yours. Every one of mine were flat. Same for the later blends (non-Wizard stamps).
Can't tell if that's dome or the angle of the disc in your profile pic. Looks like a nice thrower either way.
Cool. Yeah it is flat, that angle did throw it off a bit. A was a little surprised because a lot of older Wizards (usually Soft ones) were not flat like this. This feels like the Fossil Fuels that RDG ran in 2015-2016.