From the UK AIP (precis, not quote): The way they derive Circling OCH is by drawing arcs round each (or all) thresholds and joining them with tangential lines. Thus, for any given a/c Category, the Circling MDA should be the same for both (all) runways. However, this minimum can be sectorised so that obstacles in an area that won't be used for circling may be ignored.
To answer your question, perhaps it is necessary that you explain why, in your example, the MDAs were different.
Oh, and I certainly believe that you use the Circ MDA for the approach you are flying. How can it be otherwise? And I'm a sim instructor, too...
Last edited by keithl; 4th March 2008 at 12:14.