My simulation shows the IC surface of the heat source rising from 27.8 ℃ to 58 ℃, but my real measurement shows the temperature rising from 27.8 to only 42℃.Any parameters I can tweak to lower the simulation result？

I check the mesh, it seems good enough and the background is set to Air.

Below is the material of my heat source, I just use the default value of 5 for the thermal conductivity, I tried to tweak the thermal conductivity but it did not work. which parameter can I tweak of my PCB thermal simulation using CHT solver to match my real measurement? thermalPCBTHERMAL PCB