No fence, running substantially along a rear lot line, or approximately parallel thereto, or otherwise in a rear yard, shall exceed six feet in height measured from average grade corresponding to each eight-foot section of fencing. If such fence has decorative scalloped panels or pickets along its upper edge, height may be measured to the lowest point of such edge, thus allowing posts and corresponding elements to exceed the height limitation of this subsection, but in no event by more than one foot. Where a rear yard or side yard of a corner lot abuts a side lot line and front yard of an adjacent lot, then in no event shall a fence in such rear or side yard on the corner lot exceed four feet in height or be less than 50% open for such portion thereof which lies parallel to or otherwise substantially alongside the front yard of the adjacent lot.