In this scenario, if the pot was actually already at .1 BTC, your pay-in of .09 BTC would win a payout of .17 BTC, and a profit of .08 BTC, since you get the overages back too. (NOTE: if you use this strategy, we recommend a maximum equal to the threshold of .11 BTC per pot as any higher value is statistically irrelevant.)
1.The payout will be 0.18 and the profit 0.09BTC since you said that the overages are returned.
2.If there is at least 1 bet in the pot a dominant strategy exists and that is for the player to bet 0.11 and the reward for that player will be between 0 and 0.09
So if a player only bets 0.11 (and others are not aware of that strategy and bet randomly) he will have an average return of
0.044 BTC per bet. Edit: 0.04 BTC per bet.
3.Besides all that since you know at any given moment how much money are in the pool, you can always be the one that will push the pot to the threshold.
All you have to do after the bets are over is to show the legit transactions plus the last winning transaction that you did. Noone can't verify if the player that did the last transactions was actually a player or you.