If you were going to scale the obelisk to the player count, I'd suggest increasing Wounds not AP. The way armor works in Mothership, if you don't have something that can penetrate, the number of shots you're taking isn't going to matter. Even at 30, there's a 0.1% chance that typical starting weapons penetrate (need a natural 30 on 3D10 to remove the armor), which basically makes it impossible to damage without house-ruled criticals. Unless you have a laser cutter, in which case it becomes trivial.
(I think the Mothership armor mechanics are a bit silly and tend to house-rule them myself, but when designing a module, you kind of have to assume people are going as-written.)