You need to set an alignment point (41°) for a PT Boat at the same angle for a 90° shot, then adjust if the shot is some other angle, all the way to 0°, direct frontal shot. The exact location will vary, depending on your screen resolution and field-of-view for the game.
Divide your field-of-view (from video setting in 1st game menu) in half to find angle off center, then find the ratio of pixels for 41° off center based on your horizontal resolution. If you're running 1920 x 1080, it should be below the spotlight on the left and under 50 cal. barrel on the right at default gun position. That will be the 90° deflection shot torp release point just as the fleet auto ack begins to fire.
It's not easy, but it's easier when you have a better idea of where to aim,
Good luck!