Regarding them telling you "160 and shouldn't be changed"...it sounds like whoever you talked with at tech support does not agree with their own advertising, which says the small chamber can be run anywhere between 120 and 220. I pulled this right off the Ryde FX website:
"47 mm aluminum cylinder IFP gas chamber: Can be set in a range of approximately 50 -100 psi to allow for an initial lower “spring” rate of approximately 1 – 1.5” of shock stroke.
37mm rod cylinder IFS gas chamber: Can be set in a range of approximately 120-220 psi to allow for a stiffer “spring” rate that controls the remaining travel in shock stroke along with acting as an anti bottoming mechanism as gas pressure significantly ramps up towards end of shock stroke."
That said, you may have been talking with him about your accessory air pump...which I don't have. So he may have just been telling you that if you're using the schrader valve/air pump kit instead of nitrogen, you should put the valves only on the big chamber and leave the small chamber alone, which is why they only gave you 2 valves instead of 4. But that doesn't change the fact that there are 4 places to adjust pressure on these shocks, even if the air pump kit only gives you access to 2 of the 4 adjustments. Just be aware that your pump kit will allow you to adjust the first 1 to 1.5 inches of travel. This helps with smoothing stutter bumps on trails, but does absolutely nothing for absorbing big hits and jumps. The remaining 4 inches of travel in thes shocks are all controlled by the pressure in the small chambers, which you cannot adjust with your pump...you need a nitrogen tank and needle kit.
For this reason I didn't buy the pump kit, I just experimented a bit with my dealer's needle/nitrogen tank setup with different nitrogen pressures in both chambers, as he adjusts them for free whenever I want a change as long as I carry the shocks in. And that's where my 75/175 preferred setting came from. But like I said, everyone's different.
Incidentally, the small chambers in both my shocks were only at about 130 to 140 when I first got my sled. And many other Dragon owners reported the same. This resulted in low front end ride height and bottoming, not to mention screwing with the geometry of how the rear suspension was supposed to work, which was the catalyst for me to start my pressure experimentation thru my dealer's nitrogen tank. So if you have never had the nitrogen pressure checked in your small chambers I'd recommend taking the shocks somewhere and getting that done. Very few I know of have had a true 160 in the chambers, which is where they were supposedly factory set. Betcha yours are a little undercharged too...especially if they're OEM Dragon shocks.
