The binding is at the spring/perch interface. Ensure spring and the spring perch/seat are clean (no oil, lubrication, etc). Even shoot some brake cleaner and clean up well. You actually want maximum friction on that interface.
You may be able to add some pre-load to spring also. Not sure what the directions say as far as how much to initially pre-load the spring. If you really want you can also create a rough surface finish on that spring and and perch with some sandpaper.
Tein coilovers are JDM style system (pros and cons) that use threaded body height adjustment perch with a seperate adjustable spring preload perch. Youll have to play with that right balance of height adjustment perch and preload perch. Just be careful of going too far with only the height adjustment perch so you dont bottom out. Do incorporate some pre-load.
Disclaimer: I am speaking from my use and experience with JDM style coilovers from 2 decades ago. I do not own the Teins on my Tesla.