That’s a valid concern. It’s also why in addition to arctic silver between the copper shelf and the star, I also used lots of arctic silver between the edges of the star and the inside of the head.
Right now it seems to work fine even on turbo. The entire body tube gets hot. However, if it overheats, I’ll know when one of the driver wires on the star desolders itself. If that happens, I’ll remove the star and the copper shelf and add even more arctic silver between the sides of the copper platform and the head.
This is not my first time doing a mod like this so I have some idea what works as far as heat sinking. I did a similar mod years ago with a Sunwayman C20C, and more recently with a DQG Tiny III. The key is to use LOTS of thermal grease.