Casino logic thrives on the odds being almost favourable to the avarage player.
I'm not sure whether the developers actually looked into the mathematical effect of the odds in Harem Heroes. It feels a bit like WoW development: "don't bother with spreadsheets, just put some numbers, see how things work out, if they don't work out, try a different set of numbers."
What casinos understand very well, is, that if the odds feel almost favourable to the player, that the player is more inclined to invest beyond his planned budget, and go for a bigger reward. Or, re-invest the reward he or she already obtained. A player who just lost 15 games in a row on the other hand, is more likely to stick to his or her play-budget and call it a night when he or she runs out of it (maybe even spend the last few dollars on a drink, instead of paying that from a seperate budget).
With the Epic Days event, I was aiming for Evelyn. My target for "extra investment if necessary" was 80 crystals. The theory there, was that if I managed to get ~80 crystals in those few days, then 100-150 kobans spent on energy should be enough to get those last ~20 crystals. Well, I managed to get 42 crystals, so I quickly threw that idea of investing "some" kobans on extra energy out the window. There was no sense of "almost favourable".