...I feel as if I've asked this before, but it keeps haunting me:

Scoring for BR says "within the 1st player's deployment zone".

That should mean the ENTIRE base of a ship must be inside the deployment zone, no? That's what "within" means, right?

Correct, the whole ship base needs to be "within" the zone. Not "at".

Yes. Within is "entirely within".

At is "any portion at"