Hello Nisse,
The app Home does not even know about the offset, because it is not a characteristic, this won't change. So Home will always display the measured temperature so will Siri. We could change this in Eve but the decision is against doing so. It would confuse users that work with both apps or other HomeKit enabled apps. I will bring this up again but I'm afraid this won't be changed, sorry.
Best regards, Volker
May 5, 2020