PNG from GeoServer size on Google Earth seems uncontrollable

I have set up a GeoServer instance that hosts a lot of data that we process at work. It seems to be the easiest way to distribute since I can provide a simple network link to the GeoServer so that others can view it in Google Earth. In this case, I have a bunch of points that I have created a style for. The style is a PNG for each type. Here is an excerpt from my SLD:

<PointSymbolizer>
    <Graphic>
        <ExternalGraphic>
          <OnlineResource xlink:type="simple" xlink:href="towerBlue.png" />
          <Format>image/png</Format>
        </ExternalGraphic>
        <Size>10</Size>
    </Graphic>
</PointSymbolizer>

The sizes of these seem to be all out of whack. When zoomed out, they are tiny, but when I zoom in literally 2 wheel clicks from where the first screenshot comes from, they cover the whole screen. What could I be doing wrong here? Also, SVG didn’t work for me at all, which is why I’m using PNG.