Kevin - I would work to have properly sized rafters, and not rely on the collar tie for stiffening.
DL - all the triangles make some great bracing.
In stick framing they make a great place to hang the sheetrock. ;-)
I'm sure they are offering some sort of stiffening or bracing. The rule I've always worked with is lower third of overall vertical rise.
I'll try an throw a few examples at my FEA software and post some deflection images. In some cases on large spans I've seen bending requirements go way up at the rafter foot as the really stiff upper triangle does more harm than good (when the tie is placed too high).
