@Mike1967 cootwo. Was doing final analysis for fO2 and ppCO prior to getting wet.
If you are diving with transmitters, there is no reason to flip the tanks. You can hang them just as well with the first stages up as you can down.
The valve outlet orientation has two primary directives.
First one is SPG orientation. You shouldn't have valve facing down and SPG's pointed down as the weight of the spg's causes them to dangle and drag. If you have the valve pointed up and the spg's pointed up, your tanks have to be cocked at a pretty steep angle to clear your arm pits, and the consequence of that is they are angled equally as far down which causes drag marks when you get close to the bottom and causes them to catch on things. Doubly not good.
Outlet pointing in towards you is a good compromise for the SPG's, but can make valve manipulation difficult. Valve knobs up and you can't reach with the opposite hand and may have trouble reaching with the primary hand. Knob down and you run the risk of a rolloff in tight restrictions as well as making it annoying to hook and unhook the bungee.
Basically, your personal choice of SPG orientation is going to dictate which orientation you should use for your valve outlet.
Second will be based on your personal regulator choices regarding hose routing. If you want to use the fifth port, you really have to have them cocked almost vertically to work properly and comfortably. Nothing wrong with that at all, but be mindful with the spg's and the valve knobs. For OW stuff, it's not really much of an issue, but in a cave you need easy access to the knobs....