I have been trying to explain to a "carpenter" that putting the base on the floor makes it easier to tuck in the carpet without scrarching the base. If the base is raised, many times an installer will damage the base cramming the carpet under with a stair tool. Besides, with the base raised, sometimes the trimmer will hang up on the base. When the base is on the floor, I always tuck with the trimmer. What is your preference?