I considered the other implementation but rejected it as you'd end up with the perverse situation of players running martingales on the investment side where they actually work.  That's the problem with allowing minnows to act like big fish - you can't allow them to risk ANY portion of their balance without also allowing them to change it frequently to make it +EV.

I can't see a 'fair' way to allow different degrees of risk whilst preventing people using it to gamble (and in the process removing benefit from all other investors as well as allowing them to sit at the wrong side of the table for what they're doing).