Through extensive flow testing, we found it to be correct. While the "3-angle" valve grind (really a "seat" grind...) LOOKS logically correct, it's deceptive. But air is a fluid, and fluids don't always follow what APPEARS logical.
The exhaust benefits from a little "throating", IF there's "room". When we enlarge the seat for a bigger valve, it makes the "taper" easier. Think of the seat as a "funnel" of sorts.
The intake seat shows improved flow when the 30 deg. angle is extended beyond the valve diameter. A 70 degree throat and a TINY 45 (about .060" wide) between them will gain a little more, yet. So, in a "sense", it IS a "3-angle" job...(:- Not the tradtiional 30-45-60 deal. Of course, today, we only use that formula on stock Chevys and Fords...
It has been found at higher lifts (above .600") a 45 deg. intake face is benficial. This should be reserved for "race only" stuff, IMO. The low- and mid-lift gains from the 30 deg. face are more important.