Experience with Downfiring Subwoofer

Colleagues:

SITUATION: I own a pair of Monitor Audio Bronze W10 subwoofers. They are down-firing units. Placement will be on Berber carpet with heavy padding on a wood composite second story floor. The units are designed to have the amplifier set upon 4 feet approximately 2 inches from the ground. 

QUESTION: Recognizing the down-firing speaker radiates sound outward in all directions on the floor, what are your experiences in leaving the feet on a carpeted surface, solid platform, or on a raised subwoofer/equipment platform?

Thank you for sharing your experience and insights.