The Australian Air Services AIP has one of the most misleading paragraphs I have seen on the conduct of circling approaches and this is taken from ICAO. Discussing when to descend below the circling MDA for landing it says:
"While complying with (visual obstacle clearance) ...by day or night....at an altitude not less than the MDA, descent below the MDA may only occur when the aircraft intercepts a position on the downwind, base or final leg of the traffic pattern and from this position can complete a continuous descent to the landing threshold using rates of descent and flight manoeuvers which are normal for the aircraft type and during this descent maintaining an obstacle clearance along the flight path not less than the minimum for the aircraft performance category until the aircraft is aligned with the landing runway."
It means at night the pilot must be able to see the ground ahead and below in order to maintain minimum published terrain clearance until on final.
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.