Hello @felmue,
you are right, the top of M5Core2 and the AWS are identical. But the bottom is the challenge: The ground of the AWS shields the antenna. -> Yes, I tried the AWS version without the AWS M5GO2 bottom attached.
I tried this too:
Insert a prototyp board between AWS-top and AWS-bottom. It improves the field strength a little bit. Insert a small silver wire in the prototyp board at the antenna of the AWS-top. So I almost reach the regular field strength.