Tee emm:
While the AIP is clear in the intent that the pilot must be able to gauge his height at night above terrain, he will almost certainly be unaware of the position of the critical obstacle that dictates the MDA. Therefore, to plan on deliberately descending below the circling MDA merely to suit the ideal glide path profile downwind, or base (which has nothing to do with terrain clearance but more to do with profile handling) - has led to unnecessary risk taking because once the pilot has left the published circling MDA he is entirely responsible for his own obstacle clearance. Unless the pilot is familiar with the position of terrain (such as over water or flat ground) at night, then it is wise to stay at the circling MDA until established aligned with the landing runway.
If the MDA is too high for the pilot to remain at it until turning final and then make a normal descent for landing (while remaining within the lateral limits of protected airspace) then descent below MDA must necessarily occur on base leg or perhaps even late downwind.
The sensible answer is to circle in such circumstances only at an airport and to a runway where you have current and good local knowledge. Otherwise, you are asking for an accident.
Why is the MDA for CTL so high at some airports? Usually big rocks, sometimes a tower. But, a tower can usually be avoided by the designers by restricting CTL to one side of the runway.
Contrary to some folks opinions, CTL can easily become a high risk operation, more so at some airports than others. Less so if the pilot is very familiar with the airport environs and is at the top of his game.