Happy New Year to you as well.
I believe the number you are looking for is 180 degrees. Quoting from the read me for OLC's GUI 1.2.7 "If the ship is heading away from you then subtract the indicated angle from 180 degrees to get the correct AOB and then enter this in the TDC." In this case it would be 180 minus 50 = 130 degrees.
Hope this has been helpful. And welcome to SubSim Gerard.