Distance between 2 elements don't change anything in a thermal simulation

Hello everyone,

I'm starting to use thermal simulations in Solidworks and I need to study the impact of a heating plate on a rectangular part. My 2 parts are not in contact so I should only have radiation in my model. To detail, my heating plate is located at 1mm of my part in an open environment (you can imagine it as a rectangle floating above the heating plate). I wanted to study how the surface temperature of my part was evolving depending on the distance with the heating plate but no matter how far or close i place my part, the temperature is always the same. Worse than that, if I place the part really close to the plate (150µm) and then place it back at 1mm, I'm not always having the same result !

I already tried : Changing meshing size and type / Changing emmisivity of both part / Adding convection with different view factor/ Switching the radiation between surface to surface and surface to ambient / Closed or open system for radiation / Changing the temperature of my heating plate / Changing material of my parts.

I'm kinda stuck here, do anyone have an idea ? 

English is not my primary language, i apologize if I'm not clear on certain points, don't hesitate to ask me if you need clarifications. 

Thanks in advance for your answers ! 

SolidworksSimulation