Question about 1964 stepside rear fender eyebrow or scallop for tail light ?

[Camuchi]

I just noticed that the rear fenders only 1964 gmc are different where the tail light mounts. Drivers side has a flat recess with an arch above sure the light is mounted- positions the light at a 90 degree angle to the road.
On the passenger side it has nothing , just the curve of the fender with light mounted in a hole in the fender,makes it about 110-120degrees to the road (pointing slightly upward).

Just learning about these trucks, can some one educate me?

Thanks