It would be 165 degrees at the bottom of the hill, and I believe 195 degrees at the top(?) This is some weird mathin 3D space, but 2 vectors pointing towards each other is 180 degrees in 2D space.
I found math for the “angle between 2 vectors” on this forum somewhere. I was using it find whether 2 models could see each other, but I’m certain its the same formula here. Check this thread out that talks about it in detail. If this isn’t working for you, I can dig through my game tomorrow and see what worked for me.