I had some problems with underextrusion when using Ender 6 with top cover and speeds > 120 mm/s.
I had to move extruder inside printer to have shorter bowden tube.
This is a angled bracket to prevent bowden making sharp turns and overwhelming extruder stepper motor.
Now underextrusion close to the Z axis assebly is no more a problem.
You may need to swap cables for extruder and one of X/Y motors, or make new a little longer one
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