To amend what I said previously: Mechanical balance is not necessarily achieved by making the angles of your triangle similar/symmetric. There are other factors to be considered such as roof load distribution, rafter length, and rafter pitch.
And perhaps I emphasized balance more than I should have. Sometimes it's necessary from a structural perspective, sometimes its necessary from an aesthetic perspective, and sometimes it's not necessary for either. Sometimes there is enough structural integrity to allow compromise in favor of aesthetics and sometimes it's the other way around.

In your photo example it looks like there would be little need to place a collar on an angle unless you like the look. Would the stresses be identical at each end of the collar? Probably not. But it's not likely to make enough difference to worry about.

If I'm not being vague enough or wishy-washy enough I could get my lawyer to elaborate on this!

Cheers