Thick & thin lids : Impact on Thermal R

Theta-ja (local) = Theta jc (l) + Theta cs (l) + Theta sa (l)
From center to corner, Theta jc (l) increases, but due to 3D heat flow/ lateral heat spreading - theta cs (l) & theta sa (l) actually decrease. The resultant impact is that theta ja (l) also diminishes from center to corner.
This effect is more pronounced on thicker lids v/s thinner lids, since thicker lids allow more lateral heat spreading