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Regarding the prize pool: here's a suggestion – everyone contributes as much as they want, but, like in poker, they can only claim a portion of the pot corresponding to their contribution.
Splitting between 2 players: 70-30
Splitting between 3 or more players: 50-30-20-0-0-...
For example, 5 people made bets and played in a tournament:
Winner bet 0 rubles
2nd place - 100
3rd place - 300
4th place - 200
5th place - 300
Thus, the winner doesn't win anything (because they didn't bet).
The second-place winner claims a pot of 400 rubles, of which they receive 50%, i.e., 200 rubles. Also, from this pot, the 3rd place receives 120 rubles, and the 4th place receives 80 rubles.
The next pot, worth 300 rubles, is claimed by the 3rd to 5th places. They receive 150 rubles, 90 rubles, and 60 rubles, respectively.
And the last pot, worth 200 rubles, is split between the 3rd and 5th places in a ratio of 140-60.
Thus, the players won:
1) 0
2) 200 (+100)
3) 410 (+110)
4) 170 (-30)
5) 120 (-180)
I think this system will avoid any disputes about contributions to the prize pool and will also satisfy both the desires of high rollers and the desires of freerollers.