So, that little chip really spread out. I just gave it a new home off the sandbed to continue to encrust,
and I managed to catch it looking yellow again!
And a better closeup, from before I put it on its new rock:

Here's the piece to the left, from above:
Here's the piece that had (has) the little bit of eggcrate still sticking out. It seemed to be doing okay - not as good as Hunna's, but okay - until I went to move it to the back of the tank the other day (I did some rearranging) when I noticed an area of tissue recession about the side of a quarter or so. Not sure what might have caused it, it had been fine the last time I'd looked closely at it a day or two before:
And here from something similar to the angles it had previously been photographed from:
Hopefully I can make them happier soon. I had a bit of a nitrate crash in December, which made my King Kong Yuma start sulking, and I've been slowly trying to get everything back in better order. Running low lights for a while to try and tamp back the FHA, too, which could have been what irritated this piece of favia so much. That or maybe allelopathy from the Yuma that it was a few inches away from - hence the reorganization.