There is an additional removable heatsink between the main heatsink and the VRAMs so you may better go with at least 2 pieces of 80x40x2mm slice.
ASUS TUF Gaming GeForce RTX 3080 OC Edition
VRAM front: | 85x45x2mm |
VRAM back: | 85x45x3mm |
Between the heatsinks: | 47x10x2mm |
Pads on the side: | 66x12x1mm, 100x10x1mm, 105x6x2mm |