I was thinking of the greatest drop from any part of the public platform to any station entrance or public road or path or pavement below. I like all of the interpretations you have, there isn't a wrong one yet if I'm the judge.Do you mean the whole station, or does your criterion include those with a ticket office at ground level and platforms above? If so, Earlsfield has a pretty stiff climb (and until the last few years, no lift).