Although the behemoths of the mortgage banking industry continued to dominate sales to the GSEs in 2012, both Fannie Mae and Freddie Mac saw significantly more business from lenders outside the top tier, according to a new Inside The GSEs analysis. For all of 2012, the top five sellers accounted for 48.9 percent of single-family mortgages sold to Fannie and Freddie, a substantial decline from the 58.0 percent aggregate market share of the top five sellers back in 2011.