If the space is 0.08cm and the shim is 0.08cm won't it be too big when paste is applied? For example would it be better to have 0.07cm and then have 0.005cm of paste between each side of the shim? Or is the shim put in contact with the heatsink and thermal paste only applied to one side?

Heatsink -> shim -> thermal paste -> GPU?

OR

Heatsink -> thermal paste -> shim -> thermal paste -> GPU?