By Rob Kozlowski Source: Pensions & Investments U.S. corporate retirement plans are allocating more money to the very largest portfolio managers, and midsize and small managers face the challenge of finding opportunities in an increasingly concentrated market, consultants say. A total of 281 managers provided data on assets managed for non-government retirement plans. And as of Dec. 31, the 25 largest managers of non-government retirement plan assets — each exceeding $80 billion — accounted for $10.25 trillion, a 14.4% [...]