Hi RNP2,
There should be no changes for the angle values in the beamwidth because it is constant, it will just vary due to terrain and other reflecting factors, altho the tilt will decide on how much the vertical beamwidth will reach a certain distance, the changes will take place in the Horizntal beamwidth, It has no discreete calculation because it will depend on the terrain also and the distance that the lobes may reach, but it can be seen using prediction tools and RF tools but not in the formulas.
Regards