There should be no hard and fast rule to the angle you grind because each one of us uses tools differently what feels better to one of us will not to others.
I was speaking to an old cabinet maker many years ago and he told me "take a set of blades and grind each one of them (it was all done freehand on a stone wheel) to a different angle and make a note at the side of the wheel where you placed them, hone them and try some cuts"
I picked out two that felt and did cut better for me, he picked two different ones, he said "proves a point ma' lad do what's best for you"
This is what gets me worked up with some people demanding there is only their way of doing something there is not try the simple little test on some chisels, what can you lose a little metal, a little time, what can you gain?