You think the penus is rock hard like bone where it is really rock hard like a water balloon. Your penus contains cartilage like your nose or ears and these are floppy with a fair bit of give and this does not magically get stronger when erect it is exactly the same floppyness as normal. The hardness is blood and plasma and is just water pressure. Your body pumps water in and does not let it leave so the veins that leave the penus increases in pressure. So you have a water balloon and you think a vagina or anus are straight internally they are not. Google sex in a MRI machine and look at the images. A woman's body parts are also floppy and can move around during sex. You can see in some images with a 90° turn and you would think you would notice it but no. So basically it probably does not matter.