Grameen replicators in India, using a for-profit Non-Banking Finance Company legal form, have grown rapidly in terms of client numbers. Loan sizes are relatively small compared to per capita income, while portfolio quality was until recently very high. There is evidence in field of multiple borrowing, with clients borrowing simultaneously from multiple sources including micro-finance institutions. We build a model of the microfinance sector that explains why such multiple borrowings result optimally in small loan sizes and high portfolio quality.