Go and read "The Well Guided Bullet" parts one & two.
Boatright is concerned with VLD jacketed bullets, not cast bullets. Some of the issues he talks about may apply to cast bullets while other issues may not apply.
The short version is that a 1.5 degree throat works well with a jacketed tangent ogive, but he recommends a 4 degree per side throat for a jacketed secant ogive.
Boatright assumes that the throat angle must either match the angle of the bullet ogive where they meet, or else be slightly steeper than the bullet ogive. That doesn't necessarily apply to our cast bullets, which often have an abrupt step on the nose rather than a gentle tangent or secant.