Thanks to binocular vision, it would be more like this though :
But i don't like the idea of restricting the FOV because in a video game you don't "feel" your environment or the relative position of all your body parts, you can only see through the screen.
Yes you would be min-maxing, like in real life. Do you need more protection or more awareness?
- For a heavy shock cavalry (cuirassier/gendarme/knight/cataphract), you want the maximal protection : great helm, armet, those eastern helmets with a face plate (litchina and the likes)
- For all archers and typical eastern mounted heavy lancers/archers you want good visibility, and being able to use your bow. So you have helmets like all the mongol helms (and the Timurid/Golden Horde helm) and that tall byzantine helmet. And for Europeans, open bascinet, sallet (with raised visor, or tilted back).
- For armored infantry, you could probably sacrifice awareness for face protection, since you wear a full armor and your face is the only weak spot.
- For lighter infantry, you will NEED that awareness to avoid being hit in all your unarmored parts (see pikeman armor, and in fact everything except full armor).
You should try War Of The Roses, it's F2P (well, free demo : you have 4 default characters, no customization). It has locational damage and limited FOV for helmets. This means that hitting plate with a sword deals (almost) NO DAMAGE, But...hitting the armpit that's only protected with mail WILL.