John, I think if you talk to pilots who fly the 139 in full SAR role with a normal fuel load - OEI hover isn't an option - it seems to be a bit of an urban myth with the aircraft that is not borne out by reality.
For example - adding FIPS costs about 200kg in payload.
Having phoned around a bit, there is more to it than first appears. The earlier AW139s certainly have outstanding OEI capability, but the current model is some 600kg heavier MAUW and thus hasn't the same single engine hover at heavier weights. FIPS isn't even a consideration in our climate, but now that Ambos carry more and more gear (eg a fridge is now fitted for blood, etc) the APS weight has increased proportionally.
Regardless it is the weapon of choice for Ambulance operations here in Australia, so the operators must have done their sums and considered it the most capable option.