its interesting how seldom this sort of thing is discussed. some girls are easy to enter, others as op mentioned are difficult. some men, find missionary uncomfortable, and prefer doggy, we all have different body shapes. I found through punting, that each nationality seems to adopt a slightly different receiving posture in the missionary position, the germans seem to understand that you need to raise your knees and tilt your fanny upwards to facilitate entry, possibly due to the high no of fat folk in germany. I have a long upper body, which is good for swimming, but makes missionary unconfortable, so I prefer doggy.