Generally, all bed end flies hang over the camper trailer slightly.
The overhang is the bag section and will not affect the operation of the bed flies. The bags need to be bigger than the roof section of the fly so they can be easily rolled away back into the bags after use.
It is good to have some extra space around the bed area where the mesh of the bed end fly does not touch the beds - this helps to ensure good ventilation and avoid dampness and water seeping in through contact with the bed end fly and the canvas.
Photos with the overhang on a range of different van models.