Preheating BT much higher than DT (Bullet V1)

I do have some issues while preheating. Bean Temperature is rising much faster than the IR Drum Temp. I recently replaced my old IR-Window and the new one is shiny black, it looks almost brand new. (that was the issue in the past). the physical sensor behind is clean as well and that is definitely not the problem. Also the BT sensor is clean as well.
(I’m using RT3)