Aetna Inc.'s $5.6 billion takeover of health insurer Coventry Health Care Inc. shortchanges Coventry investors while unfairly enriching the company’s top executive, investors said in a lawsuit. Aetna, the third-biggest U.S. health plan, agreed last month to pay $42 a share for Coventry, the best performer in New York trading among medical insurers this year. The deal is structured to discourage other bidders and provides $7.6 million in bonuses to Coventry Chief Executive Officer Allen Wise, who didn’t shop around for the highest offer for the insurer, three pension funds said in the suit.