Armor Multipliers
There is a comment in the rules:
; For armor, think of it as max strength being multiplied by the number (in reality, damage is divided by this
For general modding, you can adhere to this comment. However, analyzed in detail, there are two subtile differences between a straight multiplier to Strength, and a divisor to Damage:
Damage taken
A slight advantage over a straight multiplier is squeezed out of the way strength and damage are calculated - in integers, rather than floating point numbers. Any decimals are simply knocked off. This leads to a minimal fraction of damage that just "vanishes" on every hit, compared to a multiplier variant, and can, under certain circumstances, buy the unit enough strength to take another hit.
Examples
We are assuming a tank with a strength of 1000. The tank collects a promotion crate, and VeteranArmor=1.5 is applied. The tank is then ambushed with a weapon that, after verses and everything, deals 100 damage on each hit.
If VeteranArmor was a straight multiplier to Strength, the tank would now have 1500 hitpoints, of which 100 are deducted on each hit - 1500 ÷ 100 = 15. The tank would need 15 hits to be killed.
But VeteranArmor is a divisor to Damage. Therefore, the tank still has 1000 hitpoints, but only 66 are deducted on each hit, because 100 ÷ 1.5 = 66.66666..., and as we noted above, the decimals are dropped. But 1000 ÷ 66 = 15.151515...! Meaning, after taking the same 15 shots, the tank has still 10 hitpoints left (66 × 0.151515... = 9.99999...). The tank needs 16 hits to be killed, one additional shot to kill the last fraction of health.
The examples get more extreme the less damage is dealt - if the weapon dealt only 10 points of damage each time, it'd need 1500 ÷ 10 = 150 shots on a multiplier, but for a divisor, we'd look at 1000 ÷ 6 = 167 shots! (That's a whopping 17 shot difference, for the slow among us.)
Healing
The more important or "obvious" difference to a multiplier is that ingame a unit with Armor Bonus heals to full health just as fast as the unmultiplied one does, because it has the same amount of hitpoints - it just takes less damage. Assuming RepairStep applies to units as well, we're looking at
- 1500 ÷ 8 = 188 repair ticks for 1500 hitpoints compared to
- 1000 ÷ 8 = 125 for 1000.
Now taking into account that URepairRate=.016 works out to roughly one second, that's over a minute of repair time you save through this simple difference.