So for race tasking it is a bad idea to call a task that has pilots do an out and return, 180° U-turn and turn back into oncoming traffic.
So a 0° angle between incoming and outgoing traffic certainly is bad.

What angle is sufficient to be relatively safe, 30, 40, 60?

And does this vary with the size of the turnpoint, 1 mile, 5 mile, 15 mile?

I think to make this easier to task for a CD this way it would help to have a lot bigger turnpoint list than the typical 30 points. With more points you can add steering points that create a safe turn without adding more distance than you want.

Chris