JPMorgan Chase & Co, looking to stem falling revenue in its mortgage business as fewer Americans refinance, is increasingly buying loans from smaller lenders, a practice that competitors including Bank of America view as risky. While other big banks buy mortgages from other lenders, known as correspondents, JPMorgan has racked up the biggest increase among its peers in the proportion of loans it buys from others, according to data from trade publication Inside Mortgage Finance. JPMorgan is fighting for business in what has been a shrinking market.