I think rather then selecting a custom size for the bet ,there should be custom winnings on the bet.No matter how much coins you are ready to put ,you're returns will be based on that.This will temp users to put more money to get more returns.According to me any size more than 50 cents should be allowed to place on a bet if the returns are twice the amount put .
I think that I didn't get your point , how your returns should be based on custom winnings on the bet !!
rules stay rules in all games , sometimes there are more giveaways for high rollers
for betting size I guess in dice it should remain the same , cause at the end the player will bust