I noticed that there was a “Quad/Tri Mode” in the Subdivide tool options and used that to create the crown.
Add a loop on the crown
Select top of crown edge loop
Subdivide
Toggle “Quad/Tri Mode”
Select top vertices to bring down
Translate on Z and snap to a vertex in the ring
Scale and snap to a vertex in the ring.
No spurious non-planar geometry added.
