In a long tele lens like a 600mm, the lens IS is doing almost all the work. That’s physics. For IBIS to be as effective at 600mm as at 60mm, the sensor would have to move 10x the distances, and it can’t.

Here’s a useful graphic from Canon:

The article it came from is probably along the lines of what you’re looking for, it’s here:

https://www.canon-europe.com/pro/sto...stabilization/