I'm assuming Torque to Yield bolts (measured by angle) takes the "friction" of the threads out of the equation.
If you thread a rusty bolt into a rusty hole and torque to X, it will be a different clamping force than torquing a clean bolt into clean threads to the same X value. Going by equal angle helps assure each bolt is tightened more evenly, if I'm thinking about this right. One bolt could be torqued to 350ft/lbs and the other to 270ft/lbs but they are both "clamping" the same as the head of each bolt is equal distance from the mating surface on simetrical parts.
My only issue is if there is a "base torque" before the angle, then if there is a descrepancy there (rusty bolts, mangled threads, etc), it will also be in the final torque.....correct?
If that's the case, why not clean the threads in the mating surface (since new bolts are used anyways when torquing to yeild) and use a simple torque value?
Edit: Assuming clean threads, symetrical surfaces, same torque, and identical bolt material, each bolt should yeild the same....or am I missing something?