With respect to removing the back cover entirely, I considered that the enclosed volume loads the diaphram much as an enclosure loads a cone driver. Running it open back might result in a lower Fs for the driver, but also lower power handling. Apart from the ambience added by the rear radiation, it might also result in a more open (improved) sound due to the lack of reflections and resonances. An open back baffle might not supply the optimum acoustic load to the diaphram. I decided to not significantly alter the enclosed volume. Some of the better dome tweeters have a shaped cavity and damping materail behind the dome. Perhaps this would be appropriate for compression drivers.
Perhaps the forum compression driver experts could comment on the importance of the rear cavity volume with respect to diaphram loading.

If the open back configuration is Ok, then the diaphram could be protected with a stiff, wire mesh cover (shaped over a baseball or similar object of appropriate size) with ears screwed to the back.

Regards,

AstroSonic