When shooting from a sitting or kneeling position, the Japanese longbow is held at an angle that’s nearly sideways. It takes up a huge amount of space.
Digression… something people who don’t arch usually don’t understand, because it’s not at all obvious: long arrows don’t fly straight. Although short crossbow bolts don’t flex much - they can be made of iron in fact - longer shafts have a property called “spine” which is measured and graded and stamped on the side of modern commercially produced arrows. The spine is the amount of flexibility vs stiffness.
When the bowstring is released, force is applied to the end of the arrow shaft through the nock. If it’s an iron crossbow quarrel, the amount that the shaft flexes outwards is neglible and can be ignored. If the shaft has totally inappropriate spine, it explodes into a shower of splinters (or, if it’s aluminum, it collapses like an accordion, a bizarre event I have personally experienced). If it’s slightly under-spined, it will veer off target in the direction of the bow, and if it’s over-spined, it will veer slightly less in the other direction. But in a normal shot with an appropriately matched arrow and bow, the arrow does two things: it leaps upwards and it bends into a curve sideways. Then as the arrow moves away from the bow, the curve reflexes in the opposite direction and the arrow travels through a sine-wave like path in the horizontal plane while rising in the vertical plane for some distance. The distance that the arrow “wriggles sideways” through the air before the fletching’s aerodynamic drag straightens out its path is determined only by the bow, the arrow, the rest, the fletching, and the release, so it’s a reasonably well known reasonably fixed value, but the amount that the arrow rises from the rest is dependent on the angle of each shot relative to the plane of gravity. If you shoot down from a roof or tree stand at a deer, the arrow “jumps up” significantly more than if you shoot straight at him from ground level. This means you have to aim at a different spot depending on the difference in height to your target!
Fletching matters too. A normal modern plastic angled 3-vane fletch causes the arrow to spin and makes the path go ballistic as it drops out of the rise (and historically the same effect could be achieved with straight fletching, because a bird’s feathers have different bernoulli numbers on the top and bottom) but weirder fletching (like flu-flu for example, or planing fletches, or 4-vane designs) will do weirder things. Historically you’d get different flight effects from goose primaries than you’d get from raven secondaries, or whatever - feathers vary by species, by individual feather type (primary, secondary, etc.) by age, and by individual bird.
Anyway, all this was a very long-winded way of saying that arrow flight dynamics are very complex and you can’t just turn the bow one way or another without practicing extensively first. Your aiming point has to shift, and if you are using a floating draw point you might very well shift that also, relying on your intuition and full-body neural patterning (enter Zen archery).
So among the reasons arrows didn’t get reused on the battlefield as much as you’d expect, and didn’t get mass produced as much as you’d expect, are issues of fletching and spine vs draw length vs bow draw weight. I have a long draw, due to my orangutan-like arms; I can pull a 36" arrow with a floating draw point or a 34" arrow to the lip. (Most sport combat limits arrow length to 28" which freakin’ cripples me as an archer, which is the major reason I don’t do it any more.) Real-life medieval european archers had excellent reasons to carefully hand-craft their own arrows - and believe me, the bullshit arrows that Mythbusters made from Wal-mart dowels were completely unlike real medieval arrows (and their so-called busting of the Robin Hood “myth” actually proved the exact opposite of what they stupidly claimed it did). The mass-production of arrows by the English was more exception than rule, and AFAIK only happened in time of war, and every good archer probably had a few “special” arrows to hand, perhaps painted black even when they went to war.
Anyway, because Zen archery relies on becoming mentally and spiritually unified with one’s environment, to the point where archer, arrow and target are one, it’s possible for a gifted archer to pick up an arrow, intuit the spine and fletching compensations with a single glance or by the feel of the arrow as it is whisked to the string, and shoot a moving target at any angle. The computational capabilities of the hominid neural network are truly astounding. But it took the incredibly bad Japanese longbow to make this observable… Samurai are said to have shot those things accurately from horseback! In contrast, most horse cultures used very short bows, so that the lower limb could clear the animal when tracking a target without tilting the bow. Zen archers just turn most of the conscious mind off and use their whole body as a computing engine…
…oh, dammit, I’m monologuing again. Sorry! Fascinating subject, really.