One thing to know is that the spaces below components like CPUs are frequently filled with holes that connect the part to other parts on the PCB. They’re called vias. This is because they have too high a pin density to connect all of them on a single layer.

Still, perhaps the sizes of the via pads could be adapted to these findings? Using vias to dissipate heat on other parts is fairly common, but I don’t know if current standards are as efficient as this.