Hi 4010311.
I can't give you sure, but, I think your multiplier just can be apply for the first of this spin of 10 energies, so, if you have a 5x, and spin it with 10 energies, the first of the spin would be affected by the 5x, so if it is a zeta part, or ammo, it will be given 5x. I spin my energies 1 after 1, and I use the multiplier as soon as possible (2x), I studied about the numbers and the math about the GG, and I believe that this way is the cheapier, usually I need 1500-1600 energies to build a gate using this strategy.
I will give you a link of the en. official forum of DarkOrbit, a guy tried to explain better something about the GG, and the math in the game, the percentages

, so, if you want to read, you can.
They say to spin using a ship that is full of nanohull, cause it will exclude the chance of receiving it.