How to configure this simple heat transfer problem?

Hi Mathworks Community,

I am trying to learn how the thermal simscape toolbox works , so i'm modeling this simple two geometry with with CFD and trying to get the same results into simscape however i'm not getting the same results . I know it's due to the fact that the problem is in 3D , however i can't figure out what i have to change in simscape

please find attached the problem i'm talking about

The convection is used for only the upper surface of the big cube

heat source is applied for the upper surface of the samllest geometry above