Potted cactus top texture appears "flat"

The bug

Unlike normal cactus, the cactus inside of a flower pot does not have shading around the edges of its top face, making it look odd. This is not the case for its side faces (if only by coincidence).

How to reproduce

1. Place a normal cactus
2. Place a cactus in a flower pot
3. Compare how they look from above

Expected results

The cactus in the flower pot would have darker pixels around its edges when viewed from above.

Actual results

It does not.