AE-L, AF and Recomposition with P-TTL Flash

I shoot in manual mode almost exclusively, but use P-TTL to control flash power. This usually gives good results but I'm curious as to the actual behavior of the camera with regards to recomposition and P-TTL.

Basically, if you lock focus on someone's face to provide a good midtone base for P-TTL, and then recompose, is the image processor clever enough to realise that you've recomposed? Because obviously when it fires the metering preflash, whatever was previously under your - for example - center AF point will have moved; if that's now a black or white texture, it could theoretically heavily over/underexpose the shot.

Also, how does this relate to the oft-touted "link AE to AF point" setting?

I believe that the pre flash lights the scene as is so would meter for flash exposure bassed on the recomposed sceene as the appature is the only real factor in flash exposure and this will not have changed.

Also, AE linked to AF would not have any impact in manual mode