RC_MAP_* parameters for helicopter control

Hello. I was trying to figure out how to configure the PX4 firmware for a helicopter and stumbled upon one misunderstanding. There are 3 parameter in PX4 firmware: RC_MAP_ROLL, RC_MAP_PITCH and RC_MAP_YAW.
However, the RC controller for helicopter has 4 control channels to control the swashplate and rudder: collective pitch, aileron (roll), elevator (cyclic pitch) and rudder (yaw).

Can someone please explain why the PX4 firmware has RC_MAPs for only 3 RC channels while the helicopter RC control requires 4 RC channels? Is RC_MAP_PITCH intended for collective pitch or cyclic pitch channel and do we miss one of these channels?