When they designed the car, they calculated the wavelength and the amplitude of the vibration of the exhaust past the flex point (the donut), there is some kind of resonance, which creates the droning and raspiness, then they determined the location of the resonator, but adjusted it due to packaging.
So yes, it needs to be where the factory placed it.
If you weld it into the axleback, it may have a different effect.
If you still have the flex point with the donut, but weld the resonator upstream of the donut, it may have a different effect as well.