I was going to suggest 1/8th inch drain holes, not quarter.
And you'd want to inspect them once a year, check for bugs, and poke each hole with a toothpick to clear it.
Oh, and don't forget to paint 'em, too.

. . . . probably only on the lower half of the dish . . . ?
Is the rib hollow from the center of the dish all the way to the outside rim?
If there is a joint in the rib that prevents water running all the way from center to rim, then you need to drill the holes just before that blockage.
I'm sure you can tell by inspection, where the best place would be.
And, if uncapping the ends or drilling the rim is called for, then that's easy.
Hadn't heard of anyone having this problem before.
Must not be too uncommon, so I'm surprised nobody with personal experience has jumped in to this thread.