Ok, can't resist this golden opportunity to give at least one alternate guess:
Using your experience in dealing with room resonances, you've moved the five mid settings into the range most useful for that, and so probably closer together too.
If the inductance increased a lot more than the resistance then the Q could be greater, for a more surgical effect. This sharpening might be necessary to keep the effect noticeable at lower frequencies and/or to keep them more distinct if they're closer together.
Or, all five could have all been moved to your favorite de-mudding range (and so much closer together). I can imagine someone dedicating the mid settings to suit some distinctive pickup, like the mudbucker.
Lastly, the smaller toroid is likely to be a little quieter.