Hi Thony,
Firstly, welcome to PCEkspert
Ambient temperature is always the same as the room is cooled during the summer, and heated during the winter and it varies from 22 to 23°C.
Like dh41400 said, difference in the temperature might be due to the contact through thermal paste. I had no influence in that matter since I got the setup already mounted, and the thermal paste pre-applied by AMD. I have no idea what they used, but it must be some kind of thermal adhesive since there was no mechanism that would hold the heatsink on the CPU, and yet it was firmly sitting on the CPU (maybe Arctic Silver Arctic Alumina?).
Cheers
Kreso