I’m not sure what the left/right differences are about in the harmonic analysis. IK Multimedia always seems to test out with some unusual anomaly, perhaps this makes them more “non-linear”? Their UIs always seem a little sluggish to me, but maybe that is a “non-linear” thing too. OK, this is not a review — you decide.
For a look at how the Pultec attenuation/boost trick works, see the UAD Pultec post.