That is good to know and it certainly changes the calculation on what the optimal weapons load-out is for a given miniaturization level and opponent shields.
Shield block is based on the weapon group/slot. Each weapon slot has the shield block applied to it once for all weapons in the slot. In your example, the neutron beams are grouped in a slot, so shield block is only applied once. Would the weapons be spread through different slots, shield block would be applied on each weapon hit.
I'm in a battle and 2 of my weapons hit an enemy ship with class III shields. The game log reports 22 points of damage. The enemy ship's shields were damaged 19 points, which is 22-3. However I would expect the damage to only be 16. Why 16? Because I though the shields would be applied to each weapon individually. So (11-3)+(11-3)=16.
I am not sure if you meant to group them like that or not.