How to create a High Mana "Place of Power" HQ

[JulianLW]

I found, online, in Shadowjack's House Rules, a new advantage called "Place of Power," which gives a character control of a place with +1 to RPM rolls per 1 CP, to a maximum of +5.

I don't understand RPM well enough to make a comparison. Would +5 to RPM rolls be the equivalent of raising the mana level in standard magic by a level, i.e. from low mana to normal mana or from normal to high?

How would you create an advantage that gives a mage using standard magic a "Sanctum Sanctorum" or a 177a Bleecker Street? In particular, if you say that the real world is mostly low mana with lots of no mana locations and very rare normal mana locations, how would you give a PC access to a location with normal mana, high mana, or very high mana as Signature Gear? or as an HQ?

And now as I type this, I realize the HQ rules in Supers may have something about this. I have read those rules a few times, but I remember thinking on the occasions I've looked at them that they seemed somewhat unclear; I'll take another look and see if what I'm after is there.

Anyway, are there already rules about this somewhere that I've missed? Thanks for the help, y'all!