When I reconfigure regs, I generally have two primary considerations. First, short-hosed primary second-stage regulators need to be comfortable. Second, the octo hose needs to be attached to the first stage in such a manner that it can route alongside the diver (as opposed to "hula-hooping" out to the side). Usually, these two things are related.
For example, if you connect the first stage to the valve and (from behind) the first stage has hoses at 9:00 (SPG), 10:30 (inflator), 1:30 (primary), and 3:00 (octo), both the SPG and octo hoses will tend to hula-hoop out, and the primary will not be optimally comfortable (you'll have to bite harder to keep it in your mouth, and turning your head will pull more).
If you redo the hoses such that they're coming out more like 7:30 (SPG), 9:00 (inflator), 3:00 (primary), and 4:30 (octo), the SPG and octo hoses will settle right alongside your body. Additionally, the primary regulator's hose will be in a more natural position with no twisting force applied to the axis of the mouthpiece, making it far more comfortable. (The inflator hose may rest better, as well.)
I offer this example, by the way, because it's actually what one of my buddies encountered. They bought a used rental reg from a local dive shop. It had been used for years, but the hoses looked more like a Centauri hairdo than Batman's cape. After they complained to me about jaw fatigue and the annoying octo hose (that was always catching on things in the quarry), I took one look at it, shook my head, and spent about two minutes swapping hoses around. Amazingly, the hula-hoop effect had miraculously vanished and they were immensely pleased by the increase in comfort. What amazed me most was that the reg had been a rental for years, and apparently never had anyone given a thought to how it ought to have been configured.
Different first stages have vastly different port configurations, but usually you can find a particular arrangement that is significantly better than the myriad other options. Don't assume that anything is necessarily the "right" way. :biggrin: