One of the risks of private equity executives co-investing together is an issue of management, experts said. If a company has multiple owners and it performs poorly, deliberations about how to get business back on track can be frustrating and protracted.

To mitigate the risk of an ownership dispute, Brenda Rainey, director of Bain & Company's global private equity practice, said investors are having discussions early on about financial structure, including the length of time they will manage the company and then sell it off.

"There is a lot more thought put into governance," said Rainey, "getting alignment about what actions to take with the business post-close, who is going to take the lead with value creation, who is going to lead relationships with management. All of those are more flushed out and aligned on before the deal is signed."

Lawyers with private equity clients, meanwhile, were optimistic about deals with multiple investors occurring in 2019 and beyond, saying research data may not yet reflect the activity.