RE:overlayWhich means I was way out to lunch on the other overlay. Adjusted appropriately.
Both are show together below. Looks promising.
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="https://www.opengis.net/kml/2.2" xmlns:gx="https://www.google.com/kml/ext/2.2" xmlns:kml="https://www.opengis.net/kml/2.2" xmlns:atom="https://www.w3.org/2005/Atom">
<GroundOverlay>
<name>swale</name>
<open>1</open>
<color>42ffffff</color>
<Icon>
<href>https://i.imgur.com/H4Bk950.jpg</href>
<viewBoundScale>0.75</viewBoundScale>
</Icon>
<LatLonBox>
<north>-21.09103243676966</north>
<south>-21.09803698672505</south>
<east>118.2679292905343</east>
<west>118.2576881288763</west>
</LatLonBox>
</GroundOverlay>
</kml>