when you hover over sliders in /editor -> surfaces -> Edit map get settings, it *usually* shows the percentage.
but for any ore with minimal freq I do not see that caption for some reason.
You can import the string below on that same editor screen and see if it is reproducible.
(( I do not see caption for neither copper nor iron ore on this example ))
note, you might need to close-confirm and re-open that window! after setting freqs to 17%
map exchange string for easy testing
P.S. also seems size and richness behave the same way(?)
As always, happy bug-splonking.
