Four more of the largest mortgage servicers progressed to the top of the Fannie Mae scorecard in the first half of 2012.

Nationstar Mortgage (NSM), PHH Mortgage (PHH) Seterus and Green Tree Servicing were the latest to earn higher grades compared to other firms in the group of 11 largest servicers. Seterus is formerly Wilshire Credit Corp. that was rebranded by IBM (IBM) when the technology giant acquired it in the middle of last year.

They join Citigroup (C), JPMorgan Chase [stock][JPM">, Wells Fargo (WFC), GMAC Mortgage and EverBank as the largest firms with the highest scores.

Missing from this group is Bank of America (BAC), which is Fannie's largest servicer.

Early last year, Fannie began grading 33 of its servicers, broken in three different groups based on the size of their portfolios. The government-sponsored enterprise gauged overall performance for forwarding and principal and interest payments along with foreclosure prevention efforts.

A total of 17 of the 33 graded earned at least three of four stars.

Fifth Third Bank, which is part of the group of nine mid-sized servicers, led all firms in 2011 and was the closest to receiving the highest designation under the program.

From this middle-tier group, however, only Regions Bank earned high scores with Fifth Third after six were mentioned at the end of last year.

And nine of the 13 smallest servicers graded under the program earned high marks as well.

"Through STAR, we've seen servicers make measurable improvements over the course of the program's first 18 months," said Leslie Peeler, senior vice President of national servicing organization at Fannie Mae.