Okay, so I have been working on this for a few days now and suddenly I had a revelation. Why make things complicated when a simple solution was staring me in the face. The method of reading the Margin Of Success value works for GM & Client so why not use this method for the location armour value check. This too worked, simple. No need to create a complex OOB messaging routine. I have tested this on both GM and client sides on all looks good.
The modified manage_custom_atowdmg.lua file is attached (change the extension from .zip to .lua) if you want to have a look - lines 336 to 345 in the Damage Calculator function.
I have also posted the latest version of the ATOW extension on the following thread:
https://www.fantasygrounds.com/forum...ior-RPG-Redux)
Enjoy.