A poster on another forum stated that sleeving the wire actually makes the problem worse for incandescent fixtures. The heat is mostly transferred along the conductor by conduction, not radiation or convection. The heat is transferred from the lamp base, to the fixture wires, and then to the branch circuit wires. Sleeving over the branch circuit wires would trap the heat in the conductor and make it travel farther down the conductor.
Don(resqcapt19)
