Shape.RelativeVerticalSize (Word)

Returns or sets a WdRelativeVerticalSize constant that represents the relative vertical size of a shape. Possible return values are wdRelativeVerticalSizeBottomMarginArea - Height is relative to the size of the bottom margin, wdRelativeVerticalSizeInnerMarginArea - Height is relative to the size of the inside margin; to the size of the top margin for odd pages, and to the size of the bottom margin for even pages, wdRelativeVerticalSizeMargin - Height is relative to the space between the left margin and the right margin, wdRelativeVerticalSizeOuterMarginArea - Height is relative to the size of the outside margin; to the size of the bottom margin for odd pages, and to the size of the top margin for even pages, wdRelativeVerticalSizePage - Height is relative to the height of the page, wdRelativeVerticalSizeTopMarginArea - Height is relative to the size of the top margin.

Use this property with the HeightRelative property.

ActiveDocument.Background.RelativeVerticalSize = wdRelativeVerticalSizeBottomMarginArea