Seems your bridge and neck are Gibson spaced. Rail pickups will be your best option, since I don't think SD offers different string space for its single coils.
If you don't notice a drop off of volume on the bigger strings, then it is just visual. If you do, yes, I agree, this is where rail pickups shine. SD doesn't make single coil rails with a vintage sound, though...you'd have to get something like Vintage Rails.
It's important to understand that the pole piece doesn't pick up the signal. The coil does. The pole piece simply induces magnetism unto the string. It's like a hand grenade. Close, is sufficient.
