Missing the "dy" property in LeftArrow preset shape formula

I find the LeftArrow preset shape formula from PresetShapeDefinitions.xml as follow. But I can not find where define the dy property.

  <leftArrow>
    <avLst xmlns="http://schemas.openxmlformats.org/drawingml/2006/main">
      <gd name="adj1" fmla="val 50000" />
      <gd name="adj2" fmla="val 50000" />
    </avLst>
    <gdLst xmlns="http://schemas.openxmlformats.org/drawingml/2006/main">
      <gd name="maxAdj2" fmla="*/ 100000 w ss" />
      <gd name="a1" fmla="pin 0 adj1 100000" />
      <gd name="a2" fmla="pin 0 adj2 maxAdj2" />
      <gd name="dx2" fmla="*/ ss a2 100000" />
      <gd name="x2" fmla="+- l dx2 0" />
      <gd name="dy1" fmla="*/ h a1 200000" />
      <gd name="y1" fmla="+- vc 0 dy" /> <!-- Where define the dy property -->
      <gd name="y2" fmla="+- vc dy1 0" />
      <gd name="dx1" fmla="*/ y1 dx2 hd2" />
      <gd name="x1" fmla="+- x2  0 dx1" />
    </gdLst>
    <ahLst xmlns="http://schemas.openxmlformats.org/drawingml/2006/main">
      <ahXY gdRefY="adj1" minY="0" maxY="100000">
        <pos x="r" y="y1" />
      </ahXY>
      <ahXY gdRefX="adj2" minX="0" maxX="maxAdj2">
        <pos x="x2" y="t" />
      </ahXY>
    </ahLst>
    <cxnLst xmlns="http://schemas.openxmlformats.org/drawingml/2006/main">
      <cxn ang="3cd4">
        <pos x="x2" y="t" />
      </cxn>
      <cxn ang="cd2">
        <pos x="l" y="vc" />
      </cxn>
      <cxn ang="cd4">
        <pos x="x2" y="b" />
      </cxn>
      <cxn ang="0">
        <pos x="r" y="vc" />
      </cxn>
    </cxnLst>
    <rect l="x1" t="y1" r="r" b="y2" xmlns="http://schemas.openxmlformats.org/drawingml/2006/main" />
    <pathLst xmlns="http://schemas.openxmlformats.org/drawingml/2006/main">
      <path>
        <moveTo>
          <pt x="l" y="vc" />
        </moveTo>
        <lnTo>
          <pt x="x2" y="t" />
        </lnTo>
        <lnTo>
          <pt x="x2" y="y1" />
        </lnTo>
        <lnTo>
          <pt x="r" y="y1" />
        </lnTo>
        <lnTo>
          <pt x="r" y="y2" />
        </lnTo>
        <lnTo>
          <pt x="x2" y="y2" />
        </lnTo>
        <lnTo>
          <pt x="x2" y="b" />
        </lnTo>
        <close />
      </path>
    </pathLst>
  </leftArrow>

Thank you.