I had to make an emergency purchase of a 10-spd cassette the day before PBP, so I went with what the LBS had.
It was a Tiagra-level one, and it did NOT come with a 1mm spacer, unlike the Ultegra level ones I have previously used.
This confused me, and I used a spare 1mm spacer, which turned out to be the Wrong Thing To Do, exactly as you did.
It also had rivet-heads as you describe.
Where the Ultegra has the 3 largest sprockets mounted on a spider, the Tiagra one had *most* of the sprockets riveted together into a single unit.
It went onto a Mavic freehub, using only the mavic-supplied spacer, which has cut-outs on it which seemed to accommodate the rivet-heads.
(The 1.85 is to fit 8/9/10spd onto 11 spd freehub body, IIRC)
The lockring thread engagement seemed normal, and the indexing did not need tweeking.
I didn't have time to research further!
It was good enough.
So to answer your question, I suspect you don't need the 1mm spacer with that cassette, unlike most other 10-spd cassettes.