Is Mana Enhancer limited to 2 levels?

Background: I want to make a Patron or Mentor for my PCs who must not go out in public. The reason is that this mentor tends to awaken the psychic abilities of everyone in his vicinity, especially his enemies. If his enemies get near him, they become much more powerful, and thus he must hide. I don’t think there is an easy way to do this in any system, but GURPS comes closest.

The core rules state:

Each level of Mana Enhancer (to a maximum of two) increases the local mana level by one step 

If Mana Enhancer went up to four levels, it could make a zero-mana world into a high-mana world (within a limited area). However, I don’t think it goes past two levels, and so I don’t think I can use it to justify having bad guys suddenly become more dangerous.

The campaign is not really magic-based. The game world is zero-mana. Some bad guys might have special training that allows them to use magic in a zero-mana world (possibly based on GURPS Cabal, but more likely based on GM fiat, special pleading, and flagrant breakdowns in logical consistency). Possibly some subset of the bad guys are the only people in the game world who can use mana, and they hunt mana sources like the mentor NPC.

Edit: Maybe the game world should be “normal mana” by default and I can contrive some reason to explain why almost nobody uses magic. In that event, I would need some limitation to make the mentor’s benefits apply only to his enemies. “Accessibility” might work.

Can this be done with standard GURPS rules, or does this just come down to GM fiat?