Quad in a Quad

The BLUE quadrilateral is inscribed in the GREEN quadrilateral. The points E, F, G and H subdivide the sides AB, BC, CD and DA respectively all in same ratio. Call this ratio r. You can vary r by dragging the GOLD dot. How does the ratio of the areas vary with r? You can vary the GREEN quadrilateral by dragging the large BLACK dots. Can you explain why if r is kept fixed and the GREEN quadrilateral is varied by dragging the BLACK dots, the ratio of the areas of GREEN to the BLUE quads does not change?