There isn't a necessarily "preferred" tension. I'm not 100% sure about the flexpoint but go with the recommended string tension for your first time. If its not enough control for you, try raising your tension 2 pounds or so at at time and judge how much control you're getting from it. Continue raising the tension until you either hit the maximum tension recommended (it'll be on your racquet throat) or find a comfortable medium.
Also, if you're using a very stiff string like Big Banger or Babolot Hurricane, you might be experiencing a LACK of power and that may contribute to your problems..