The original formula for calculation of the amount of received wounds is rather illogical. In one hit you receive from one to three wounds, with the exact amount being absolutely independent from the amount of damage. You can receive 3 wounds if the threshold of 10 hit points is exceeded by just 1 HP, and at the same time you can't get more than 3 wounds (in one hit), even if the hit has dealt 50 damage (suppose your soldier had 60 HP, so he survived that hit). Furthermore, that 50-damage hit can leave you with 1 wound with the same probability as with 3 wounds! (And an 11-damage hit can leave you with 3 wounds with, again, the same probability).
It bugged me a lot, so I decided to make this tweak that distributes the wounds proportionately to the lost HP. If I were more meticulous, I would even made it so that the amount of wounds received grew with the lost HP exponentially (like the difference between 0 and 10 lost HP would result in 1 wound, but the difference between 30 and 40 lost HP would mean about 5 wounds), but being lazy as I am, I just went with even distribution: for every 5 HP lost you receive 1 wound, as simple as that. This, of course, is also true for all units that can be wounded (if you enabled "Alien bleeding" in advanced options of the game).
There is one difference between the aliens and the humans though: humans will die the moment they have 10 fatal wounds, even if they still have some HP left. I decided against extending this mechanic to aliens, since most of them are either mentioned in UFOpaedia for their survival abilities, like Snakemen, or are enhanced in some way, or, in case of Ethereals, are not even supposed to be able to survive without their psychic powers (which would also enable them to withstand fatal wounds, I suppose). The only species for which dying upon receiving a certain amount of fatal wounds would make sense is Sectoids, but they already have rather few HP, so I didn't want to make them even more wimpy.
The mechanic with 1 wound per 5 lost HP should work on all weapons, even those added by other mods. The mechanic with 10 fatal wounds works only as long as you use vanilla armors, so if you have some additional armors from other mods, you would have to make the adjustments yourself. (Or you can leave a comment here with the id of the armor, and I would add it to the list). I also covered the civilian armors (including the civilians from the "Armed Civilians" mod), in case you increased the amount of HP civilians have.
In case you want some weapon to be more/less likely to inflict wounds, you can give this weapon a tag SPECIAL_WOUND if it does not use any clips like laser weapons or melee weapons. If it has a clip, give this tag to the clip.
For example:
items:
- type: STR_SOME_WEAPON_OR_CLIP
tags:
SPECIAL_WOUND: 1
- type: STR_SOME_OTHER_WEAPON_OR_CLIP
tags:
SPECIAL_WOUND: 2
WOUND_FACTOR: 3
The weapon/clip with "SPECIAL_WOUND: 1" would either use the vanilla formula for wound amount, or you can adjust it with "damageAlter" in this item's ruleset as explained here:
https://www.ufopaedia.org/index.php/Ruleset_Reference_Nightly_(OpenXcom)#Power_and_Damage_typesand here:
https://www.ufopaedia.org/index.php/Ruleset_Reference_Nightly_(OpenXcom)#Item_Damage_TypesThe weapon/clip with "SPECIAL_WOUND: 2" needs to be given one more tag: WOUND_FACTOR. The value you assign to this tag means how many hitpoints will be lost by the unit damaged with that item before a wound is inflicted. For example, "WOUND_FACTOR: 3" means that the item will give one wound per three HP.
I wouldn't be able to create this mod without the great help from Yankes.
Upd. Attached version 1.1