Driving faster can help the wing extensions, dirt rolls over faster.
Dad made some from old car or truck leaf springs, bolted on the top corner of the bottom where a extension would go.
Rarely see them or the cover boards around here on any plow. I agree a cover board would make it more prone to plugging. They do help tick in the trash tho, leave a blacker field.
As mentioned a 12 inch bottom just comes from the factory ready to plug, not much room between bottoms. Good, big, well adjusted coulters help a lot. Not old worn down ones.