Google Earth Enterprise overlay

I wrote a new class implementation for cesium native that supports google earth enterprise map overlay as a Cesium for unity component. I have based it on top of BingMapsRasterOverlay class.
the component displays the map tiles right to the zoom level so it seems.
The problem is a small offset on the y-axis into the wrong world coordinates in the mapping projection, as far as I know, Google Earth Enterprise supports Mercator Web WGS84 just like Bing (and Google) Maps.

For example: coordinates of Taipei city gets an East China Sea tile map close the China coast.

Please advice as we couldn’t figure out what would be the differences in coordinates tile creation google earth enterprise.


The implementation in CesiumJS might be useful as a reference:

Beyond that, I’m not sure what might be wrong. But if you shared some screenshots of the problem, something might jump out at me.