If half of the portfolio fails (a good outcome), the cashout option would need to be 2x the original investment for them to break even. More if failing companies are likely to use up the entire line-of-credit and successful companies are not.
Setting the payout to be a percent of revenue might work, but could also kill a company with thin margins. Setting it to be a percent of profit will encourage companies to post zero profits. I'm not sure what the other options are.