Confusion about network structure

<img width="451" height="680" alt="Image" src="https://github.com/user-attachments/assets/72fa0739-954f-4ff5-8cd4-e7cffb2b7dd0" />

I noticed that in YOLOv12, the A2 attention is only enabled in the A2C2f modules within the backbone network, while those in the head network do not have attention enabled. What is the purpose of setting it this way?