I had the exact same problem with a fsa orbit headset (installed on a wabi frame) and fixed it the same way. In my case it is pressed "cups" rather than machined into the frame. This makes me wonder if it is an issue with either the compression ring or perhaps a combination of tolerances between the OD of the steer tube and compression ring being off just enough to cause this issue.
It makes me feel better that someone else has had this issue and solved it the same way.
FYI fsa sells micro spacers to fix this issue if 1.5mm is way too much.