Bounty percentage is low even with the best paid projects. 2% of total supply dumped would not make a significant price dip. The reason why some ICO prices tank after getting listed on exchanges are insitutional early investors and founders. Early whales with big bonus percentage also contribute to the fall, like people who only bought to flip.

Another reason for dips is marketing vacuum. People get whipped up by the marketing campaign during the ICO, which stops after the money is in the coffers, new supply of people that want the token dwindles and prices tank, then one big announcement and they fly. No announcements and they die.