Private equity firms are turning increasingly to add-on deals in their quest to mitigate the impact of frothy valuations, often looking to them earlier in the investment cycle. Many firms find it tough to avoid competition and steep valuations for sizable platform deals. But small tuck-in deals often come cheaper, which helps lower a platform company’s overall valuation multiple. Private equity-backed add-on deals hit a record $310 billion so far this year through November 4, exceeding the $274 billion for such deals during all of last year, according to data provider Dealogic. The spike comes amid near peak purchase price...