prepky, I seriously doubt your size per se is complicating things all that much, but its understandable you took those "extra steps" to assure every possiblity of insemination. I have read over the years about, how to better assure success, women might want to do exactly as your wife did and lay still and stay in similar positions as you described. Don't feel too silly or ashamed about your sharing this with us. I don't believe any of us are "sex experts" ...or is that "sex-perts" ?
The possibility of having a low sperm count is nothing to be ashamed of either--should that be the case. A simple test would do wonders for just helping you know for sure! If you should prove low, it isn't a kiss of death or a blow to your masculinity. It's no more than another "health matter"...that's all.
Getting pregnant is a shared project of course. BOTH of you have to have things in good order and working favorably! It should be taken as no disgrace should either of you find something even slightly amiss which more than likely can be remedied without too much ado. Many couples seek medical counsel and it saves them winding up becoming overly wrought--frustrated with each other and near starting the blame game. So, don't let that happen! There's so much (new!
wisdom out there in medicine about "making babies" (helping couples get pregnant) that in thinking about it here, it seems a shame to waste that info (if it could help you.)
Getting pregnant is always a matter of "things being just right"....timing (with her cycle) and just the shear miracle of Mr. Sperm meeting Ms. Egg at just the right precise moment. Nonetheless, even the healthiest, most fertile couples still have to allow for favorable conditions from both partners' efforts. Remember, it's a shared experience. Your size shouldn't directly determine impregnation potential.
While there could be some unique considerations perhaps... or, not--, if the semen is indeed entering her vagina; and the sperm are plentious, healthy, and mobile! then as a man you're certainly doing YOUR part!
There could be some undetected reasons within your wife's "inside tract" which complicate your sperm being able to join her eggs...alkaline levels out of whack, other "body chemical imbalances", that kind of thing goin on which again, an MD could help figure out. Don't give up. But, don't delay seeking some wisdom either, if you continue to see no results. This subject is too important to each of you personally and to both of you of course, as a couple. There's a kind of a deeply engrained (quite natural!
psychological need in each one of us...just KNOWING that we can procreate, if we ever want to. And, that's why this matters....so much.