well, if you're stood up at one end of the bedroom & the girl is sat down the other side of the room, that could well have an influence on the chances of conception.
Try not being on the phone or a 69 or with another girl etc.
Cover all known impossibles and by deduction you should be left with a really strange position involving pulleys weights and an Aardvark , that might just get someone pregnant, possibly not human though!
A point's been made there - and no, you're not being smutty Ethel. Having the pelvic area tilted often helps - providing that the female's ovulated in the first place!