holy kaw!! Don't mess with that gas reservoir! Pressures vary, but 165psi is about normal.
The sag needs to be set like matt sez. That's total drop of bike measured from completely unloaded..lifting up on the fender to unload it...to you sitting on it with all your gear. 100mm (4") is a good place to start. Adjust by loosening the locking spanner on the shock spring, then turning the spring (not the spanner nut) to increase/decrease preload as required.
When you're all done and have your 4" of 'race sag', check the free sag. That is the amount the bike drops under its own weight from the previously mentioned completely unloaded position. Should be 1/2 to 1". If it's much less than 1/2, it is an indication of a too soft shock spring. If it is much more than 1", it is an indication that your spring is too stiff (not likely. The stock kdx spring is 5.0 kg/mm which is good for about 185#).
Don't think this is odd. All bikes need to be set to proper sag according to the weight of the particular rider.