Hello I just got my first real arf setup, a SU-31 ep by black horse models and it says to balence the airplane 80 mm behind the leading edge of the wing so i hold it upside down and add weights to the front and i finally reach ballence but then take the weights out and see that i had added 4 1/2 ounces to a plane where the box says that it should weigh 2.1 pounds is this normal?