at the *actual size* of the relation and takes that into account when scaling the statistics (see table_block_relation_estimate_size() in tableam.c). If the table sizes don't match between the two servers then there's no guarantees the planner will produce the same plan.
Sorry that I didn't see this thread until now. I would like to note that table_block_relation_estimate_size() determines the actual size of the relation by asking pg_class, and the relevant values there are set by pg_restore_relation_stats().