The primary function of shower sex is not to get clean. It’s to get dirty. Hair washing, shaving one’s legs, anything that doesn’t add to the erotics is secondary. Now having said that, a loofah-off or armpit shaving can add extra spice and rev up the overall production. It should also be noted that it’s best to be fairly clean before having sex. There’s always a moment to sneak away and wash a ball sack or soap up a buttcrack.
Sex in the shower usually falls under the category of better idea than practice. In movies and books it’s the stuff of magic. In reality it’s often the stuff of fighting for the heat, stepping on toes and trying not to break an ankle or hip. With enough passion between the two people and/or the influence of alcohol, often the difficulties of shower sex get overlooked and the mere fact of, “Oh, cool we’re having sex under a stream of lukewarm water” is enough to make the event a success.
Now, as to short girls and tall guys making love in a tub: Doggy Style and its various incarnations is your friend. It sort of evens the playing field and creates less of a stand-up-game. Depending on the size of the stall, and your man’s thigh control he can also lean back and lower his junk to a more favorable position for insertion. Also don’t knock bathtub rim sex. If his ass isn’t too boney, he can sit on the side of the tub and you can sit on him. Also there’s always him lying in the tub with you on top while the shower goes. That’s what we in the biz call tub-shower-sex.
If all that fails. You are not screwed. There’s also this for sale. Plungers –sex shower handles. you can use that are specifically designed to make shower sex more pleasurable – more functional and less an act of trying not to break you or your partners neck and libido.