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.