Is there an advantage in filling surface mount bollards with concrete for reinforcement?

All of our heavy duty bollards have at least a 5mm thick wall (beware of cheap alternatives). The weakest part of a heavy duty bollard is the point where it attaches to the ground, filling it with concrete will do absolutely nothing to its structural integrity.

On the other hand for below ground bollards concrete filling will make significant difference to its strength when used with appropriate reo rod as well.