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And I would usually say it has to be close to a 50/50 division.

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Your statement is divorced from the underlying use of the concept and isn't right or helpful. WAWB is usually (not always, but usually) relevant to a situation where you must decide how hard to push your hand. If you are either WA or WB then you don't push as hard because it means that you will win the least (because your opponent will likely fold to a raise or re-raise) or lose the most.

I don't think the relative likelihood that you are WA or WB has anything to do with it.