I'll attempt to answer this one....
Sex is a "learned skill" over time and what works for one couple may not necessarily work for another.
Yes, the "missionary position" is the customary man-on-top way to go and the woman can vary the depth of his entry by just positioning her legs either straight out together, wide apart, or bringing her legs upward, bending at the knees. A pillow beneath her hips also adds to her comfort. Bottoming out (hitting the cervix) is not the most pleasant sensation for many women. Men measuring from six to seven inches and beyond in length seem to have this matter to consider more than others. The average LPSG man here (8 to 9 inches or better) will almost surely have to REALLY be careful to avoid hitting the cervix. A few around here have indeed reported having reached the uterus as well! It gets serious from that point sometimes.
The "woman on top" position is suggested often as a means to allow the woman to get used to her partner's size by allowing HER to grasp and introduce his member into her gradually at a pace most comfortable for her. It's also a position which seems to allow him to "hit her clitoris more effectively" to some degree. The man can "stay still, or wiggle his hips just a bit--whatever....(i.e. whatever works!
Men are cautioned though that injuries to the penis occur more often with women on top. Sudden unexpected moves (by either partner) have been known to cause penis fractures. Obviously, take it easy!
"Doggie style" (rear entry) has been said to be the "ideal human sexual position" and even has been said that it was the original INTENDED sexual position by some experts who study such things! "Doggie" seems to provide mutual pleasure for both partners and is often less demanding in expended, exerted energy. Doggie seems to provide a more "fluid, rhythmic movement" for the man to maintain as such. It also affords better overall stimulation for the woman's genitals using a "rear entry approach".
All the info above is generally true but each couple is different. Some of these positions however, may quite simply not be all that comfortable, or possible! (for physical reasons unique to the individual person).
Most couples who enjoy a good sex life typically use a variety of positions and do not adhere to just one exclusively for the most part. Again, it seems "whatever works best" for the individuals involved. There is no "standard" as such...just a knowledge of the basics---well practiced over time. Quite simply stated though, many of the larger size men like represented around this forum will simply have to be more careful (than average men) in using their full lengths regardless of which position they're trying. Their depth of entry will have to be monitored considerably, as well as their thrusting. It's one of the consequences of being "above average".