Every investment in the portfolio must be carefully monitored for trading cost, internal commissions, turnover, and bid/ask spread cost. It falls on the shoulders of the plan sponsor to prove that these fees are justified and prudent to pay inside of the portfolio. All these costs are not available in the prospectus, an independent analysis must be performed to determine what these actual costs are. The total costs can be daunting.
It actually states in UPIA that any time you deviate from mutual funds or asset class portfolios that are derived to get market returns (with very low turnover) the burden of proof falls on the person who does not use Modern Portfolio Theory.