Okay, I think we are talking in circles here... a lack of communication about what exactly you want, what you currently have, and what you know.
Try this. Make yourself a script called "fire.sqs". Inside of that script, write the following:
arty dowatch [getpos target select 0, getpos target select 1, 100]
~2
arty fire (weapons arty select 0)
exit
Next, name the vehicle that you want to be firing "arty". Then, name the target you want it to fire at "target".
Use this line in a trigger's "on activation" field in order to run that script:
[] exec "fire.sqs"
Now, try running the script in your mission. Watch how the launched missle/shell whatever lands. Then adjust the number 100 in the script above, until you can get the weapon to hit properly. If the arty is shooting past the target, lower the number. If it isn't shooting far enough, then raise the number. After enough trial and error you will be able to get it to hit.
One note: this will only work when the artillery and the target stay in the exact same positions! If they move, then you will have to find a new value (instead of 100 or whatever you ended up with). If you want to make a script that will work no matter where the target or shooter are, then it will be more complicated, but first start out by getting the above script to work.
PS: The script of mine you linked to doesn't work with vehicles. Once I finish that script, I'll make a version specifically for vehicles.