This is a common problem with a fairly simple solution.

What I teach is that if a guy goes tight waist/ankle off the whistle to use rotating back pressure towards the trapped ankle side combined with you posting on his wrist that has your ankle. Keep his wrist posted, get hand control on the tight waist side and you should be out no problem. you can finish wish a switch, hip heist, stand up and a myriad of other combinations. The main thing is to keep his wrist posted on the mat, dont pull it to your waist.