Yogani touches on a stage 5 kechari in his AYP book with the tongue going back towards the throat. After exploring a little it seems that different ways of sitting or lying down guide the tongue in different directions. With the head down or in chin pump the energetic direction of the tongue goes in the direction of the septum or nostrils such as stage 3 or 4 , with the head up in sitting meditation the tongue wants to relax more in stage 2 and stage 5 seems to some into play lying on the back in corpse position. Any other kechari position seems to add stress in this pose except turning the tongue back towards the base of the skull and the throat rather than forward towards the nostrils. Since it is corpse relaxation naturally the tongue would be relaxed as possible.