Midsized RIA firms are the new sweet spot for managers of mutual funds and ETFs, according to a new report. That means there is likely more opportunities for advisors in these midsized firms to get some extra help from the money managers' sales arms.

According to new research from Cerulli Associates, the growth of RIAs is changing the priorities of the asset managers' sales forces. Cerulli estimates that RIAs will have grown their market share to 14% market of advisor-held assets by the end of this year. Money managers have traditionally been targeting RIA firms with assets under management of $500 million or more, neglecting smaller firms.

But the firms with $100m to $500 million in assets are, in fact, exactly the ones money managers should be courting, because their advisors are the ones using mutual funds and ETFs the most.

However, although the money managers throw the most resources at the RIAs - up to 16% in 2011 - they generally dedicate their resources to the largest firms. Those with $1 billion or more are the "sexiest," according to Tyler Cloherty, a Cerulli analyst and one of the report's authors.

Ironically, because those firms have better internal research, many of them are relying less on managed funds and managing the assets on their own. Meanwhile, the midsized firms, with fewer internal resources and limited staffs, use mutual funds and ETFs more in portfolio construction. These products account for nearly half of their portfolios - an allocation nearly 10% greater than the portfolios of the bigger RIA firms.

Once the money managers' sales forces catch on to this missed opportunity, Cloherty said, they should pay more attention to the middle-market RIAs. "We're trying to get them to focus their efforts downmarket because they're underserviced," he said.

And although RIAs at firms of all sizes claim they don't want to take sales calls, in reality, they like a little attention, according to Cloherty. "They like to know who their wholesalers are and shake their hands once or twice a year," he said.  The like to pick the senior sales reps' brains for new research and investment ideas.

Once the sales reps realize the opportunity at midsized firms, Cloherty believes the RIAs should be able to parlay it into extra support. That could include more manager research and investment ideas, and money for marketing support, including funding for client acquisition events. Some RIAs even have sales reps come in to talk to clients about specific investments or give general market commentary. He said these visits with clients are more rare, and are done largely in support of variable annuities or other complex, big-ticket products.

Elizabeth Wine writes for On Wall Street.