Below is a screen-shot image from JDeveloper with the property inspector of the panel stretch layout.
<af:panelStretchLayout id="psl1" topHeight="auto">But please note of the following description of the topHeight attribute from the <af:panelStretchLayout> documentation:
the height of the top facet specified as a CSS length or auto such that this facet will no longer be stretched and instead will consume the initial offsetHeight given to its children by the browser. It is important to note that in an average page, a switch to a layout using automatic heights exhibited a 10 percent degradation in initial layout speed in Internet Explorer and a 5 percent degradation in Firefox. Results will vary but it is recommended that you use this sparingly in order to optimize your page. Also an automatic height will cause the facet child to not be stretched both vertically and horizontally. If necessary, you can make that automatic height child stretch horizontally by specifying a 100% width in the inlineStyle of that child. Note that many components such as the panelGroupLayout with layout set to scroll or vertical will have their own built-in stretched widths by default.