Ran into this one recently and the solution came out of left field, so I thought I'd throw it out to the internet at large. I've got a server which is running php-fpm and nginx. However it has several websites running on it, each of which has its own php-fpm/pool.d/ profile. We were having a problem with one of the websites, which got a lot more traffic than the others, so we needed a way to monitor its php-fpm performance.
Setting up php monitoring is not hard. There are many guides around the internet. You put the line
pm.status_path = /status
in your fpm pool file, then add a block to your nginx config so that it can only be accessed by certain IP addresses.