Detached by the Impact
"It was surrounded by debris belonging to other parts of the airplane" added the BEA [informant]. "The protected container or memory module is normally attached to the chassis. But this module is much heavier than the chassis. No doubt it came apart from the impact" with the surface of the water, explained to AFP the Director of BEA, Jean-Paul Troadec. "The container has a much greater force of inertia, it is quite possible that the container followed a different descent trajectory than that of the châssis because of currents", he explained further.
Sounds perfectly reasonable to me.
I would propose obtaining a similar recorder and memory module to chuck over the side to see where they end up -- how far apart and bearing would be useful.
Well it would be considerably cheaper to remove the expensive innards of the boxes, add pingers and ballast to bring the weight back to spec before chucking overboard
Don't forget to bend the chassis frame the same as the original.