Simple answer: it doesn't!
More complex answer, obviously to be able to use block clone the blocks have to be on the same ReFS volume. Since SOBR represents extents of different storage, there's no real way to take advantage of ReFS enhanced synthetics with this configuration. To use ReFS + SOBR it's highly recommend to use data locality policy, however, even in this case there's a few things to look out for, specifically, if any extent fills up, and backups are redirected to other nodes, you will lose the enhanced capabilities for merge and/or GFS. Also, if you evacuate nodes, block clone is not preserved, so if you have mulitple block cloned synthetic fulls in a chain, they will require space for each full in the target.