I don't really understand how you could partially win or lose as you put it. It would be a loss for everyone as far as I can tell.
Example for what I meant by partial win :
You bet 1 BTC at odds of 2 decimal for player to finish in the top 5, but as it turned out there are 6 players sharing the top 5 spots, so your payout of 2 BTC is multiplied by 5/6 for a total payout of 1.66666666 BTC. It's still a win but it's a partial win.
Sorry to jump in again but the only reduction occurs on the player's tied for 5th. A 1/2 reduction............... The poster should win without reduction.
If the bet was on the player to finish exactly at 5th place and he shared it with another player then you'd be right.
But
the bet was on player to finish in one of the top 5 places, regardless of which exact place in the top 5, and since there were actually 6 such players, the dead heat rule was applied to all winners.
There are two important things to note here :
1. Our rule is stated very clearly with example and it is a universal rule.
2. The bet odds was factoring the possibility for a dead heat in the way we lay out in the rules. If the dead heat rule would apply only if Rory McIlroy finishes 5th and share this spot with another player as you suggest, then the bet odds would not be 1.02 but rather there would be no bet at all because such a possibility was non existent.