I believe that you both need to be assigned as pilots of your respective ships, and both need to be in the cockpit.
Its also possible that sensor sharing is restricted to factions (ie factiohn-faction sharing and PC-faction sharing) since the example given does seem to only give faction stuff.
Both of us are assigned to our respective ships and the rules state:
"Ships, vehicles, facilities, droids, and stations share sensors with each other when they are friends, have an active pilot and are not disabled."
The part about factions are giving examples of when you'll be able to share sensors, or so I thought...
I'm pretty sure there is a bug with sharing sense between IFF allies, I can no longer use sysats owned by a faction I have set as an ally and who has me set as one. I've been waiting for someone else to report it because I'm lazy.