There are now comments at wowhead that the 9.2 Torghast souls (Bat, Dragonhawk, Elekk, Pig, Tallstrider) also appear on lower layers (lowest mentioned is layer 4). Seems like the souls can appear on all layers !? (Maybe higher layers increase the chance, but that's just speculation.)

Removing the layer constraint from the "Torghast 9.2 Soulshape Guide" should do the trick for now.