I'm in the process of tweaking my Model 11 Polks as well. While you were inside the speakers, did you notice dark foam baffling glued to the inner chamber underneath one of the mid drivers? Both of my speakers, which look like they've never been opened up, have this below the 'inside' driver. Since these are mirrored pairs with specified left and right speakers, by 'inside' I mean to say the driver closest to center. The baffling has broken down due to old age and one has fallen down to the bottom of the cabinet where all of the white baffling is located under the passive radiator.
Does anyone have experience replacing these? I'm wondering whet function they serve. My guess it that they partially seal off one of the upper chambers, but I'm not certain. How important is it to find the same material as a replacement?
Here's a picture of the foam baffle on its own: