Presenters from the Employee Benefits Security Administration went into that very issue during a 2015 webcast series, spelling out a fiduciary’s responsibilities relative to plan costs, including their duty to make sure fees and expenses paid by the plan are commensurate with the level and quality of services being provided.

Read: 7 things fiduciaries shouldn't say in court

In other words, both cost and quality are important.

However, fiduciaries often consider costs in isolation, the study said, and that leads to problems.

They pay more attention to cost or to the potential for litigation, their other major fear, than they do to investment merit when making decisions for a plan.

Class action suits over excessive fees that have drawn major headlines have helped to push them in this direction.

So lower costs look more attractive, particularly since sponsors are already worried about fiduciary liability. “There is an unfortunate misconception among plan sponsors,” the report said, “that low cost equals low risk from a fiduciary perspective. As such, the industry’s focus on reducing fees supports continued flows into low-cost, passive products. Asset managers feel this pressure, with 50 percent identifying increased demand for passive funds as a major challenge to winning DC assets.”

The report added, “Advisors and consultants must remind plan sponsors that choosing the lowest cost option, which is most commonly passive, is not synonymous with carrying out their fiduciary responsibility.” Cerulli also pointed out that collective investment trusts (CITs) carry lower costs for those plans large enough by plan assets to qualify for them. While some criticize CITs because they are less stringently regulated, “Cerulli believes that lower compliance, marketing, and operating costs combine to make CITs attractive in the current fee-sensitive environment.”