I propose a 'Default Win' amount.
This would be in addition to 'Default SP' but could be an alternate for 'Default Back'.
My request is based on the scenario in racing where you want to wager proportionally to win a set amount.
Example after a race starts you want to back the three leaders after 200m due to a perceived track bias perhaps.
The Horses are $21, $4.5 and $8 in-running. Using a Default Win of $100 my wagers will be $4.76, $22.22 and $12.5 with a clear profit of $60.51 before commission.
I imagine their could be a setting to chose whether you want to use a default level stake or default to win.
Your maximum exposure will protect you if you accidentally click a $1.01 or you could have an additional protection of a minimum price.