“They’re so tall,” said Steve Cohen, founder of Point72 Asset Management, as a woman on stilts, covered head to toe in leaves and flowers, loomed above him. “It’s hard to have a conversation.” Cohen and about 570 other guests mingled among the woodland creatures Wednesday night at the Rainbow Room, joined later by male dancers with their bodies painted blue and green -- all in an effort to make Lincoln Center’s annual Alternative Investment Industry Gala a hot ticket. It seemed to work.