am I to late to jump in, maybe its gone off topic but from what we tested in oz at a mates workshop with external positions was that the external placed in a good position so as not to interrupt gas flow and cause turbulence was the best place to mount it a nice flowing angle off the manifold would not hinder the flow off the gas therefore making the turbo spool faster if ya need proof look at HKS manifolds and the angles with which the externals are mounted.... Another form of boost control is to use a blow valve so that it leaks at a certain point have seen it done like this a few times very different but just as effective