I have to note that by further research it is showing some weird behavior. If you station only one marksdwarf in one splitter he will not miss most of his bolts. But if you increase it to two dwarfs their bolts will miss virtually 100% of the time. And even weirder is that when you remove the newly added dwarf the first one will continue to miss all of his bolts. I guess more SCIENCE will be needed.
It's stuff like this I think would be helpful for Toady to hear about. It's odd behavior glitches like this that can often help illuminate where buggy code might be hiding. I think FPS death is likely strongly linked with minor bugs in pathing, item stockpiling, job ques etc. that are magnified by the shear number of incidences of these bugs that occur as a fort grows.
For whatever reason, I've come across an issue. The archers will eventually just stop shooting at whatever is in the pit, like they lose sight of it. Regardless of whether it's a Minotaur, a troll, a trog, or something else. They shoot at it happily for a while, maybe a few seasons. This particular one worked up until creating two Elites. Then it just stopped working. All that changed between particular choice of target is whether civilians got interrupted or not.
Although I haven't tried to build this archery range I remember running into this buggy behavior in my old fort on the DF version that came before this one. I had various insect men such as lice men which basically served as my live fire targets for my archers. I let them loose in the shooting gallery and my dwarves would rain bolts down on them from behind some fortifications. It seemed to work great for a while. Lice men are incredibly durable when it comes to taking crossbow fire. I had some of them that survived in that shooting gallery for many seasons and then I noticed my dwarves simply stopped firing at the long lived ones after a while. I figured it was an ammo problem until I investigated more closely and realized they had ammo in their quivers. They just stopped firing regardless of which method I used to order them to attack the lice men. Since it happened a while back my memory is a little faded but I remember sometimes I could get a few of them to start firing again if I disbanded them, made them go back to their regular jobs for a while and then ordered them back to the shooting gallery.