Feanor you get it.

All drivers I've encountered have an open throat which extends through the voice coil to the rear of the speaker. From inside the throat folks may not realize that the voice coil area appears open and cylindrical and not like a flat coil.

The large permanent ring magnet at the rear magnitzes the screen plate further down the throat which holds the phase plug's metal washer ( or counter sunk screws ) in place. There is zero cone mass or moving mass as the phase plug makes zero contact with any moving parts. You can place your fingers on these solid wood phase plugs while playing and feel no vibration.

I think E-Stat has my phase plugs confused with some pointy Dagmar dust caps. I'd recommend sacrificing an old driver for some speaker 101.