Custom Supports not created as expected

[davethomaspilot 0]

I'm trying to get a support structure for a small overhang, the area circled in blue:

 

 

 

 

 

 

So, I added a custom support:

 

 

But, when I  look at the preview the support structure is not there.

 

 

When I enable creation of supports in print settings (with or without the custom support structure added), I see this in the preview"

 

 

 

 

 

Note the support stops about 1 mm below the overhang it needs to support, maybe because of the nearby overhang and associated geometry?

 

Is that 1 mm gap ok?  If not, how do I create  a support struct for these overhangs?

Edited November 11, 2021 by davethomaspilot