Keeping multi-GPU rigs cool?

As a newbie to building computers, been having issues trying to figure out how to cool my rig. The problem is that as the heat gets shunted upwards, each card gets hotter than the last (eg 31C -> 38C -> 42C -> 44C. At load during things like video generation, the hottest card can reach close to 90C). Trying to search for answers online or via chatbots has been not very helpful, given the 3D nature of the problem and the unique nature of each person’s setup.

Tried using riser cables to space things out and move GPUs to the empty dead space next to the side fans, which failed miserably (seems like the mobo doesn’t like long 500mm cables). Tried to arrange case fans to help cool GPUs with limited success, and I’m unsure of which direction to point the case fans (point at GPUs to help cool them, or point them away to draw away heat?).

Any thoughts on how to effectively keep GPUs cool?