Well for carving tools, the answer is pretty dang simple: whatever angle makes it comfortable for you to hold.  
Agree 100% with that statement.
I don't set the angle to a particular value.  I just put the cutting edge on the abrasive and adjust the bar until my hands are in the position that I typically use when carving and lock it down.
Agree 100% with that statement too. Great minds and all that.

Andy -- Old Chinese proverb say: If you think something can't be done, don't interrupt man who is doing it.