Fast & flat is where its at for coyotes.
With every inch of barrel you cut, you negatively affect bullet drop & wind bucking ability when trying to engage an ever moving critter, at unknown distance, in the wind...
I'm with Grimstod, gimme a long barrel! If I were afforded the luxury of a can, I'd still keep my barrel choppin' to the 22" range, for the simple fact of not hamstringing the ballistics of any given cartridge.
Unless you're having to stick a rifle out the truck window constantly, the longer the rifle is, the better!
Being that you have a can, I'm sure you can tell how much more smooth & easy your rifle is to aim with the can on, as opposed to off? The extra rifle length is like having a longer wheelbase on a vehicle, makes for a much smoother ride...
If all your shots are <200yds, then a short barrel might not be much of a hindrance. But if you're wanting to clean up those tricky ones that hang up in the 2-400yd range, you're gonna want all the muzzle velocity you can muster to mitigate range guesstimation on the fly. And that longer barrel is just gonna sit still on the stix, better...
If coyotes were static targets that would let ya sit there, range, dial/hold & shoot 'em, then muzzle velocity wouldn't be such a priority. But, they don't, So...
Short barrels & maximizing cartridge performance is a slippery slope. If you're really wanting an 18" barrel, then do it. I'd recommend making sure you know what you're leaving on the table, performance wise...
Given your leaning for a short barrel, I'd stick with a lighter weight bullet, and push it fast as possible to help make up for the inevitable velocity loss from the shorter tube. IE 55-70gr bullet in 6mm, and no bigger than 95gr in the 6.5mm...
Just some thoughts to ponder, have fun with your new rifle!
