16.5.2 specifies that patrol markers cannot be stacked, however in the context it seems to mean "stacked with other patrol markers". Is that correct? Could a patrol marker stack with other non-patrol FWA units? For instance, I could see myself placing a 1/9 patrol to recon a hidden move marker, or to be used as a spotter for bombardment, only to later reinforce such a hex with its associated company, or with other FWA units.
Correct. Patrol markers can't stack (or be adjacent).