Too many requirement but the prize itself is not clear
If i bet 0.0001 btc with 70% chance -> My prize will be very small
If i bet 0.0001 btc with 30% chance -> High risk, hard to get my money back. My prize can not compensate for the money I've lost
I think you need increase your prize to gain more dicer...
0.0001 is the minimum value, according to what OP posted (and there's no maximum), Unless OP changes that later. Currently by what is posted, if you make a 0.01 at ~%50 and end up being a winner, You will get 0.01 and etc...