Can someone confirm where the sliding should take place between the rear caliper and the carrier. Mine is stuck solid!

Should the caliper slide on the pin or does the pin slide within the carrier. (The front slider pin that has about a 6mm allen key head).

Last night I had convinced myself that the sliding is between the carrier and the pin but looking this morning I am not so sure.

calliper slides on the pin, or should do

If anyone else suffers a slider seizure - the pin is fixed to the caliper and should slide within the carrier!