20% nitro is not needed at all, i hover on 0% nitro all the time (it works just as well if not better than 15%)
i wouldnt tune it any different than you would your normal sports plane, the key for 3D is getting a good transition because most of the time you are not hovering at full throttle, so if you richen the high end too much it will affect your transition/ mid range which is where you hover.
after a flight or two you should be able to tell if you need to richen or lean your high end, just listen to the plane when it is in the air, it will tell you what it wants