I just added a "E3D Titan Aero" kit to my Acrylic Prusa I3 Bro B - it looks fine so far...

After all the needed changes the first prints showed a problem with the extrusion and after a few houres of investigation the situation is as follows...
The new hotend uses a 104GT-2 termistor. I knew it and changed it in the firmware as documented in configuration.h (5).
If I measure the temperature now in parallel externaly i have a stape 20% lower temperature as shown on the display (or in software).
I already searched around a lot but found nothing... has someone of you an idea?
Nice greetings,
Martin