It wont be coming from the mouthpiece if it is new, and finetuning it will not wolve wet breathing. This is the design of the regulator (like most others) that are designed to function best in the faced down horizontal postion. Most divers do not spend too much time on their backs and alot of regs have this problem It is just a matter of water and pressure physics.
As for the IP creep. I know that it is something serious but it wont blow up your reg or anything. It will just puff out of your second stage when it gets high enough.... nothing you cannot notice, end your dive and have resolved.