Sorry I was late to follow up with this old thread. Thank you all for your opinions and advises.
First of all, I don't recommend anyone to shoot any coyotes with any calibre and power, especially with an 18gr pellet at 32 ft.lb. I did managed to drop a coyote with a (lucky) perfectly placed head shot to the temple at 70 yards. It was a very rare and unique situation for me to pull that shot off partly because the coyote was sitting still and not much movement when I finally squeezed off the kill shot. It was my first coyote shot with my Crown with an 18gr AA pellet.
My question was "would this power and calibre enough to kill a coyote with a perfectly placement shot?" Absolutely. The coyote's skull is very thin and if you are able to hit anywhere in the head/temple area, the pellet will penetrate the skull and impacting the brain.
Please watch this video where I showed the damage of the two coyote skulls with pellet vs slug. Since I have shot three coyotes with slugs, I would never use pellets again. The slugs would cause more damage and more energy dump into the brain with a head shot.
Obviously, there are many variables and potentially bigger margin of error to hunt coyotes using a .22 calibre gun like I am using. But my argument is that if I am confident with my ability to hit a small target at any set range and if the opportunity is there to do so, then I will take that shot; Otherwise, I would just reject the shot and wait for another opportunity.
So far I have gotten 4 coyotes (70 yards being the furthest) with my .22 calibre air guns, all with a head shot. I agree that higher calibre and more power would be better, but the end result is still depends on the placement shot by the person behind the trigger.
Thank you all for your comment.