If your top fans configured as exhaust add this vent cover to the back to improve airflow.

This way you can cool your GPU much better by sucking in air from the back/PCI slots and exhausing hot air at the top.

Combine this mod with this to achieve a reasonably good airflow in the DarkFlash DK100 PC case: https://www.printables.com/model/587739-pci-slot-cover

Tested with RX 5700 XT and Asus TUF 6700 XT. Both cooled efficiently after adding these mods.