In Keysight's popular AN 150 there is a plot of noise and harmonics amplitudes versus the level of the input signal at the mixer (page 57).
It's stated there that the maximum n-th dynamic range is given at the intersection of the noise and n-th harmonic lines (i.e. when both noise and the n-th harmonic are of the same amplitude).
I'm having a hard time understanding why this is so. As I see it, one can change then level of the mixer's input to perform some kind of trade-off between SNR and harmonic distortion. So what criteria is followed to state that when both effects are equally relevant the dynamic range is maximum?