I don't think humidity is the issue. Turning it up too high may cause you rainout.
It seems that you are mouth breathing, your jaw is dropping while you sleep. You will need to use a chin strap, or a soft cervical collar, or start to train yourself to use the tongue seal technique.
Place your tongue to the roof of mouth with tip of tongue behind front teeth. Suck upwards gently.
This places your tongue in a natural position which will stop air from escaping. This takes practice to master.
This air that is escaping from your mouth is what makes your mouth feel as if it is filled with cotton.
As far as your machine being set wide open is not helping. I don't know what the makeup of your Apnea events are, but I would raise the minimum pressure up to 6.
Can you let us know what your 90% pressure is, and the breakdown of events: Obstructives, hypopneas, clear airways?
You will do better if you used #SleepyHead software.