Two People Sex Positions #2 - The Ajar Door
Straight from the Kama Sutra, this sexual position always reminds me of when cars that could talk back at you first came out onto the market. Many cars would ding and have little lights that flashed and, sometimes, purely for the sake of your annoyance, the car would say in a soft, seductive car-femme voice, "your door is ajar." This was such a silly and novel idea to people at the time that it became a running joke and I, thinking I was such a clever little child, would retort, "no it is not a jar, it is a door!" It would be years later before I would be exposed to the Kama Sutra and this position would bring those memories of doors and jars flowing back so that now I think that there must be a niche, at least someday, for a porn in which every time a woman spreads her legs really wide that seductive car-femme voice would come back and the viewer would again hear that familiar warning, DING! "your door is ajar." And that, dear friends, is one of the main goals of this position, getting the penetratee's legs wide enough open for some good from-the-behind direction holey-humping.

This position essentially entails that the recipient be standing and leaning forward on something with their legs spread wide and one knee on whatever she's leaning on so that the giver can, well, give. The fucker stands behind the fuckee in a way that makes penetration the easiest. This is a good position for the recipient to contract their pelvic floor muscles easily and for the giver to take advantage of the position for stimulating any sensitive part on the front of the recipient that they so choose. Then again, the recipient may object to a thumb in their bellybutton, so please at least have some form of courtesy in however you decide to take advantage of this position. Stimulating her clit will, of course, make her wet and more ready for some deep door-humping action and you can perhaps jiggle her tits with a hand or tease a nipple if you're into that sort of thing. If you're not into that sort of thing, you can always put your hands on her hips and help guide your movements and hers in time to whatever rhythm you happen to prefer, even if that rhythm happens to be to the beat of Rick Astley's "Never Gonna Give You Up," which had been stuck in your head all day.
Much like any position, this one can be modified to suit the needs of the individual according to sexual preference and kink. More flexible people might be able to modify the position some by putting their foot on the chair instead of their knee, opening the door up even more, so to speak. Less limber people might want to use a bench with a back on it instead of a chair and individuals with a bad back may want to lean on a higher surface than the back of a chair (leaning on a counter top with your knee in a chair may work or using a tall dresser with a stool or chair or perhaps you can find some giant sized smurfs around the house somewhere). In contrast, more flexible people may even be able to not use the back of a chair and may just put their hands on the floor in front of them instead ... but that might actually be considered a whole other sex position entirely (and might be one that you should get doctor's approval for before performing if you're not used to doing activities that require such strain - don't worry, he won't mind the mention, but he might want a visual representation so that he doesn't get confused). Whatever you use to lean on, be sure that it is at least stable item of furniture as you don't want to later have to explain precisely what you were doing when you managed to strain all your muscles in your groin and right leg (though, telling them that you injured yourself trying to get your door ajar could result in some great stories for posterity).