I've always been under the impression that 'knee-chest' position is a variation on the all fours position where the person being positioned lowers their chest to the same surface as their knees are on - floor, exam table, bed, whatever.. This increases the exposure of 'certain areas' ;D . The business of pulling one's knees to one's chest I have experienced when laying on my back; but I have never heard of it being referred to as 'knee-chest'; but it makes sense to call it 'knee-to-chest'. This practice increases exposure, especially of 'one particular area' ;D . It will also do so if one is laying on one's side, or if one is kneeling, bending forward so one's chest is touching one's knees.
Just thinking about it stirs me inside.