This Bass Exciter works in one-way phase, wich also can be inverted, but that so unlogical to me.
While one phase is 'exited' other is un-excited. Atleast it should be unchanged. Bass clippers and clippers in rest of processing already makes this un-excited bass so it will be even worse for one of phase atleast.
That's not really how this works. But, I have just checked what happens if I just tilt the phase a bit and then the waveform is mostly symmetrical again, which is indeed much better. So I'll add that - for the 2nd harmonic only, probably.
Edit: The 3rd harmonic looks best if it's inverted (that makes the waveform much less spiky), but due to some imperfections in the filtering that removes some low frequency content. I'll see if I can fix that as well, that would really make things better. At -12 dB (the default) it doesn't really matter much - only at levels close to 0 dB it becomes very noticeable - so I' not sure if this will help at all, but it's probably easy to solve so it's worth a try.