First I want to thank you for this great app and sharing it for free
Thanks 
why you don't make joystick ball to turn in circle instead of square like it's now
To get full range at 45°, 135°, 225° and 315°, the joystick moving area HAS to be square.
With a circle, at 45° max values would be 71 (100/1.414) assuming a -100/+100 data range.
Please let me have your phone/tablet model