With banks starting to issue jumbo mortgage-backed securities instead of holding originations in portfolio, the sector has expanded beyond the two nonbanks that propped up non-agency jumbo MBS issuance since 2010. The activity shows favorable economics for non-agency MBS, including tighter spreads on interest rates between conforming mortgages and non-agency jumbos. The average interest rate on a 30-year fixed-rate conforming mortgage was 3.596 percent this week, according to Inside Mortgage Finance ...