Does anyone have any thoughts on whether failing to prove FCO (Fair, Consistent and Objective) would count as maladministration?
I would be wary of the concept of failing to prove, as this doesn't mean it didn't happen, just it is not easy to confirm. It would be easy to turn this upside down (which other side could do) and expect you to prove it failed.
Obviously individuals reviewing would formulate their own view, but I think you are going to be on a dodgy wicket if other side shows they tried to comply and you can't demonstrate they didn't. Fair isn't a yes/no concept, at the other end of the spectrum is unfair which is clear enough, but at what level does fair becomes almost fair is a grey area.
Finding some obscure point which was apparently skipped or missed wouldn't be proving unless you could also demonstrate that it was critical and therefore the overall judgement was wrong. Although it may be worth a go, something like this tends to be a collection of parts, and not all parts are needed to be obvious what it is (bit like a box of chocolates, if a few are eaten, you wouldn't think of it as box of something else). Just because you may consider they could have gone further (and considered other factors) it doesn't confirm the conclusion was wrong (other factors could have been borderline relevance).