The idle gate position should have no effect on ability to achieve full throttle. Its purpose is to limit minimum throttle to flight idle in flight and automatically engages on take off. As you mention, it automatically disengages on landing to allow for ground idle.
If it is stopping you getting full throttle then maybe that’s linked to the throttle mapping issues that people are reporting that can sometimes be fixed by disengaging and reengaging the flight idle stop.
Also the OP has noted the recommended fix for this known bug. Rotate Power Management Knob to MCP and back to TO restores full power.