After my last post, I realized the very thin spacer was from the bent, not my 700c wheels and also
checked my two remaining 1070 11-28 cassettes NIB, neither has the very thin spacer. The take-off
cassettes were Shimano, both with the thin spacer. I also have a spacer separately packed and
lableled meant for adapting 8-9-10 spd cassettes to an 11 spd hub. Measuring both the thin
spacer is indeed 1mm thick and the adapter spacer 1.85mm thick. I stand by my original opinion
to use the thin spacer if you like the resulting axle to cassette spacing on the R side of the hub,
rmove it if you feel more space is needed for chain clearance when on the small cog to the inside
of the fork.
Using the thin spacer to get the preferred cassette position on the hub like you suggested makes sense. Thanks.