Hi Paul -
I would consider covering any or all parts of the metal ribbing of speaker baskets, to suit your taste. I would personally cover all of the metal basket. I don’t think you could over-do it with fo.Q, unless you happen to like metallic ringing and distortion as part of the sonic blend (some do!). The basket isn’t really technically part of the transducer therefore it shouldn’t be vibrating at all. Maybe start with one 20mm strip on each rib to see if you like it. If you like it, adding more will give you more of what you like.
Because fo.Q deals with low amplitude vibrations very efficiently, it is not subject to the same sonic pitfall as other damping materials (or at least to a much lesser extent). Namely, absorbing certain frequencies but leaving others behind to dominate and muddy the sound.