You could use one of many things to fill the gap, jb weld, devcon, abs paste, filler, paintable silicone, or you need do is fill the join, you can sometimes find small clay modelling tools at craft stores, help to get in nice and tight. All the above are albe to be sanded, perhaps not the silicone (depends on make)
You could also add some white paint to the rim of the mic tips
Correct Aerators/Hovi-MIX tips are present. Screens used shall be of a wide type mesh, with the rim of the mic and the inside white or painted white.
I added a couple of links to your other thread about SDS upates