Fannie Mae and Freddie Mac had wildly different experiences in the first quarter of 2018, a period when both firms saw declining single-family business volume. But Freddie’s production of single-family mortgage-backed securities plummeted 29.2 percent from the fourth quarter of 2017, while Fannie’s 5.7 percent decline was roughly one fifth as severe. Those cross-currents upended the playing field, giving Fannie a hefty ... [Includes two data charts.]