Used to be that it automatically fires if dodging fails and you still have some block points. Now it rarely happens to me. Are there new mechanics in play now?
Melee skill and reaction score matter, and you need an actual source of block (either MA arm/leg block or weapon block tech).
Oh so that’s what limb reaction score is for.
Is it never a 100% chance even when my head and eyes are unencumbered at all?
At perfect reaction score it becomes a sure thing at melee 5.
Handily you also seem to block with your most armored body part (in the case of arms at least) either that or it defaults to lower arms since I’ve noticed blocked attacks almost always reduce damage from basic zombies to nothing as soon as you get some type of arm guard even if it only covers the lower arms.
Its probably 'cuz arms and leg guards are flagged as blocking items, and they tend to have good blocking stats compared to most weapons.