In Practice Mode, try to set up your phone as much to the side as possible. That gives SmartPitch the best view of the flight of ball, for measuring Pitching or Hitting. Here's a diagram for Pitching.
The Best Position, in Green, is level with the Rubber (zero feet back) and 21 feet (7 paces) to the side. Enter 21 and 0 in the Practice set up screen.
OK, but sometimes not as good due to position of the sun or cloudiness of the day, is the Medium position shown in Yellow. That's 15 feet (5 paces) to the side and 6 feet back from from Rubber (2 paces). Enter 15 and 6 in the set up screen.
SmartPitch can work if you put the phone 9 feet (3 paces) behind the Rubber and 9 feet (3 paces) to the side, but if lighting conditions are marginal, it is harder for SmartPitch to pick up the moving baseball from here. Enter 9 and 9 in the set up screen.
Avoid putting the phone behind the rubber if possible.
It is best to set up so the sun is on the same side as the phone. If the phone camera is pointed into the sun, the bright glare can hide the baseball and make it hard for SmartPitch to see the ball.
Remember to swivel and the phone on the tripod so that you can see both the Rubber and Home in the phone's view panel.