The value you are suggesting above works for all melee/ranged weapons. Some crit values are weapon specific. A single weapon has a crit value of 19.
The code I was trying to use is as shown, in the weapon properties, crit range 15 eg. If he is attacking a creature with AC19, he rolls 15 and gets a crit, but his attack bonus is +1, so his attack result is 16, less than AC19, so the attack is a miss. But as you can see from the image ALL 'crits' say they hit (prob from the normal expectation that it is 20 and 20 is always a hit)
Attachment 33126