The spacer is placed to have the best chainline, i.e. to have the chain no too much deviated on the first and last cog.

The original 10s cassette has 9-10-11-13-15-18-21-24-28-32 so all cogs are smaller, the 3 bigger are each 4t smaller than on the XT 10s 11-36t cassette 11-13-15-17-19-21-24-28-32-36.

The cassette I have is 11s 9-11-13-15-17-19-21-24-27-30-34 and there is still space between cog and swing arm on every sprocket (but difficult to say for how many teeth more)..

A 11s is about 2.9mm wider than a 10s cassette which is I think what provides the space between chain and swing arm and avoid rubbing (the biggest 11s cog is about 2.9mm closer to the center of the wheel, the next ones a little less because the spacing between cogs is slightly smaller for 11s than for 10s).

And for the same reason, i.e. a 12s cassette being even wider than a 11s cassette, the 12s SRAM 10-36t 10-11-12-13-15-17-19-21-24-28-32-36 cassette should work without rubbing.