Circling areas have been surveyed to provide guaranteed obstacle protection

Are you quite sure about that ?

I'm not a procedures designer but was closely involved in the past with my ops engineering escape procedure work. Unless things have changed, I suggest that the only accurate data will be associated with Type A and similar charts. Most of the EOL (STODA) data, for instance, is either taken from available topo chart data or inclino survey .. again, not as accurate as you might think.

For I/F circling, the protocol used to be that the proof of the pudding test post letdown design was not much more than the checking pilot's flying the circling area at the circling minima and looking with the Mark I eyeballs for any obstacles of note ... not quite the same as a detailed survey, a lot less accurate .. but reasonably fit for purpose. Obviously, the procedure is better worked if the aerodrome environs have been surveyed for whatever reason .. just don't presume that this always is the case, though.

In general, be VERY careful about thinking "guarantees" when it comes to obstacles .. even where things are published post-survey, administrative errors can sneak into the published data .. it's ALWAYS a case of user beware with any of this stuff.