...if you own $500 of a $1000 loan which defaults, your default rate is influenced more strongly than a user who owns $25 of the same loan. We'll be adding some help text to make this distinction more clear.
Not quite. For any given loan, the Default Rate is the
same for all lenders on
that loan. For example, the $500 lender would have received half of the repayments made, while the $25 lender would have received 2.5%. If the borrower had paid back $800 before defaulting, the big lender would have received $400 (losing $100) and the mini-me lender would have received $20 (losing $5). Default Rate = $100/$500 = $5/$25 = 20%.
What matters is the proportion of a lender's ended loans represented by that default. If the big cheese had only that loan, the overall lender Default Rate still would be 20%. If the small change lender also had $500 in ended loans with no other defaults,
that overall lender Default Rate would be DR = $5/$500 = 1%. This also is a good example of why portfolio diversification helps spread out the risk of default for relatively small portfolios.
Edit Note. Okay, so I can't subtract.

The punch line stays the same!
