[Gaz64]

Finally somebody has posted "the right way".

Have done it that way many times, my own logic.

Logic says 90 degrees at half lift is correct. It allows the smallest width contact patch across the valve stem from closed to max lift and back to closed.

The rocker tip swings in an arc. If the tip travels from 2 o'clock through 3 o'clock at mid lift (90 degrees to the valve stem) to 4 o'clock at max lift, the travel ACROSS the valve stem is a shorter distance. The shorter the distance travelled, the less loading on the valve stem and guide which prolongs component life.