To use a very simple example:
Investor A has 10 BTC, sets risk at 0.25%
Investor B has 10 BTC, sets risk at 1%
Investor C has 10 BTC, sets risk at 2%

House roll:
30 <= 0.25%
20 >0.25% and <= 1%
10 >1% <= 2%

House roll for all bets <0.25% is 30, making the max bet 0.075
For bets between 0.25% and 1%, the house roll is 30 for the first 0.075, and then 20 for the rest: so the max bet is 0.225.
For bets > 1%, the roll is 30 for the first 0.25%, 20 for the next 0.75%, and 10 for the final 1%: total of 0.325

So a better comes in and loses a 0.075 bet:
Investor A gets 0.025
Investor B gets 0.025
Investor C gets 0.025

On the other hand, a better comes in and loses a 0.325 bet:
Investor A gets 0.025
Investor B gets 0.1
Investor C gets 0.2

Edit - added 0.25% bet case.