Your valance must look like and be shaped like the
white piece that is shown on the left side of  photo #2
This piece uses the largest slot on the clear valance corner.

The small white piece shown on the right side of photo #2 uses
the smaller slot on the clear valance corner.
This piece is called a return.

Photo #3 shows the clear corner attached to the valance and return.

Valance front in photo #3 measures 3-5/8" high.
Measured from top of clear edge to bottom clear edge.

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