Interesting. The grille material Jon Oakey uses - I just cannot hear any difference with the covers on or off. Absolutely none. And this is from a person who always removed grilles from speakers he has used in the past.
TBH I think Jon said it is the same as Apogee used. Can you say the same of your grilles? If so, I am amazed you can hear a difference.
Does it look like this?
The other reason I thought you may not be using the front panels is that pure foil tweeter excursion. It is immense!
View attachment 28182
Something similar, but I seem to remember the one on mine was a bit more dense !
The ribbon's excursion was large, but not quite enough to hit the grill