Base curve or surface is a "helper" surface, not the target.
Add one more surface, like a flat plane, the size of your source pattern.
It can be directly below, and touching the source pattern. Could color it green, to help in selection...

The ring is the target, you only need one...

(part of source cut away to show green rectangle planar)
(I'm an amateur, so the other guys likely have better help.) :-)