When I see drawings or read stories of people getting a digital rectal exam, they seem to be either on all four, either on their back legs open. I do not know whether that's medically accurate.
In my case, I had two DREs when I was a child for suspicion of appendicitis, and each time I was sort of in the same position as for pooping in a squat toilet (and actually was told to bear down as though pooping). If I remember correctly, the physician approached me from the front and put her gloved hand under me. I've never seen anybody else on this site mentioning this position - is it only used for appendicitis diagnosis, only used for children ?