Depends on the position of the critical obstruction that affects each runway. Quite common to see different circling MDA for each runway.
Dunno about that, Centaurus! The PANS-OPS circling area is defined as tangents joining arcs from each threshold. I reckon there can't be an obstacle that is unique to only one runway's circling approach as the circling area as defined applies to all runways.
Sorry to come in so late on this. The only reason that a circling altitude is different on one rwy approach to the reciprocal is that you have made a circling restriction AND that restriction encompasses part of the final or missed approach protection area. In this circumstance, you can not exclude obstacles affecting final or miss as part of the circling evaluation. So an obstacle you can exclude on one approach may not be for the reciprocal direction. Ostensibly, this means every procedure can have a different circling altitude to the same aerodrome. In Oz, the circling altitudes are common across the aerodrome to prevent confusion [as demonstrated above], except where an infrequently used procedure would unnecessarily raise the altitude to an unreasonable value. The Cairns NDB or VOR -B is a good example
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