I have done ballistic tests on expired 8" thick bone-in hams and pot roasts at 200m and there is complete penetration with .22lr subsonic ammo. Sometimes bullet bounces off bone and fragments, other times bones shatter. Cow/pig bone is a lot more solid than a coyote. What do you consider adequate?
For me, adequate, is a round that does not need the target to be at an exact, known distance, before I have a decent chance to hit it.
No matter what the bullet may do IF you hit it, you have to hit it first.
Short of pinning the surrounding area with dozens of range marking stakes, there doesn't seem much of an answer for it. Quiet, and effective, are pretty much mutually exclusive.
If you can legally and safely shoot the animal at night, it seems reasonable to do as decent a job of it as you can.
I can tell you from some long past experiences, that pretty much nobody hears a single shot, let alone has much of an idea where it came from. You are only going to GET one shat at a coyote in the dark, unless you are busy trying to shoot it inside a hen house or similar, so noise isn't as important as the OP think it may be (or, he isn't going to shoot anyway) while safe backstops and knowing your arcs of fire in the darkness is VERY important.
I shoot a fair number of CCI Quiets, and for the use I put them to, they work pretty well. But trying to reach out past 50 or so yards becomes an exercise in Kentucky windage and hold over, as does shooting out past 100 yards with High Vel ammo in my 10/22, unless I dial in out at that range, which is OK in the gopher patch, but makes my rifle not very useful for the purposes I have it for here, around the yard.
What's the drop on a sub-sonic between 50 and 100 yards, with a 50 yard zero, or a 100? And is it reasonable to expect a fella to be able to accurately range a coyote in the dark, accurately enough to hit one for a decent kill?
In the OP's position, which is pretty close to mine here on the farm, other than the population density there, I suspect, I reach for my .223, as if I can put the crosshairs on it, I can hit it at any range that seems even a little bit reasonable.
Cheers
Trev