
I've never thought about it, but have you ever asked the question: why many positions that we can see in the innumerous books about Kama-Sutra and similar editions are practically stupid? Well, the first example I have on this same photo.
Look at this part I cut from the photo from Footiam's post. If you watch it attentively you will agree with me: the figures are depicted upright, not horizontaly, I want to say, not in bed in other words.
All we here are adult persons, so I think you understand me: is it not crazy? Is it possible to have pleasure at least for one of the 4 characters of the scene, or to make babies in this position?
Here it is. (I think it is very plausible even if I am not completely sure that it comes from there)
Vedas told: if you want to have a special reincarnation as your baby (manifestation of a Buddha or Bodhisattva etc), you have to make it in a special position. This position -every time specific- was suggested to the future parents in the temple, I think. This is the reason of "stupidities" we find in many "specialized" pictures.
My thoughts about it:
can you imagine how laughd the prist after he suggested something similar the position on the photo? At his place I would make everything to assist the execution...