A decrease in the size of collateral pools supporting some jumbo and Alt A mortgage securitizations coupled with an increase in the size of the largest loans included in such pools puts loan concentration risk in the spotlight, according to Moody’s Investors Service. In its “Sizing RMBS Large Loan Concentration Risk” report, Moody’s said large balance loans generally add more risk to a securitization as the pool size shrinks. And loan concentration risk takes on…