It doesn't matter what the candidates have as their second choice, they only have one vote apiece. There'll be some Cooper voters who went for her because she's a woman who'll have put Corbyn as second choice, and some who went for Burnham because they think he's a more realistic leftish candidate who'd have Corbyn as second.

If Jeremy does get 40% of first preference votes, the chance of him picking up enough on the second choices to push him over 50% would be quite good. The thing is, even more than in normal elections, no one has a clue.