They have mentioned the new heatsink design here first: Introducing the Framework Laptop 13 powered by AMD Ryzen AI 300 Series
It sounds like the new design will be used in the future and it was revamped for better performance (quiet and cool). I am sure they have tested it before and found it to be better. That is why it is curious that we see a worse performance than before. I would suspect it to be at least the same or even better.