I like the idea of +2 for a going “on the defensive” action, where a character in melee is using a weapon, a shield, or their hands to only make sure they do not get hit. I would only apply this against ranged attacks if the character had a shield.
You could also have a +2 “defensive movement” action where the character is trying to move in such a way that they are avoiding incoming attacks. This could work against ranged attacks or melee. If the player is trying to get somewhere and not stand relatively still, you could reduce the distance traveled if the player is running a serpentine pattern against ranged attacks (LoL). (Insert Serpentine! Serpentine! meme here)
I know this isn’t a simulation, but I teach HEMA and Filipino sword fighting, and we cover being on the defensive through both the use of weapon and / or shield as well as movement (but usually both tool and movement, though each work separately, of course). I can sit “toe to toe” with an opponent and focus my actions not on attacking but specifically on making sure I am not getting hit. I can also play Muhammad Ali and just use footwork and body movement and position to make sure I am safe from incoming attacks. Occasionally I use both as a way to set up my own attack. So if you use Both, you could have a +4 option against melee attacks, and if you had a shield, you could have a +4.
This is a long winded answer to say, I too like the +2, +4 thing, I just add an additional +2 option…