AFC have absolutely no say whatsoever where the mics are to be placed, unfortunately.
They are placed around the field of play and up in the gantry for crowd noise, so at an OF match they will be pointing at the OF fans so they are generally the only people you'll hear. Despite this, the atmosphere at the rangers game was rank anyway so it wouldn't have picked up much if it was pointed at the RDS.
Oh, and many of the mics are boom mikes; they're connected via cable to a hub. Just isn't viable to have them stretched all the way up to the RDS Upper so people on the telly can hear some fans sing.
Much easier and simpler to have them placed where the cameras and commentry team are, which is in the South Stand gantry.
But no, AFC have no say where the mics go