2.1.1429 Part 1 Section 21.2.2.3, applyToSides (Apply To Sides)

a.   The standard states that the applyToSides element specifies that the picture shall be applied to the sides of the point or series.

In Office this element also specifies that the picture shall be applied to the floor or the side wall but is ignored on the back wall of a 3D chart.