It seems to be that the slots are filled with a very limited amount of variation...

Top Row is always the dungeons
2nd Row is always lvl 50 24-man, lvl 60 24-man, Random Alexander Gordias/Midas, Random PotD floors
3rd Row, Garuda/Titan/Ifrit Ex, Mog/Levi Ex, Shiva/Ramuh Ex, Odin/Ultima
4th Row, Bismarck/Ravana Ex, Coil 1-5, Coil 6-13, PvP