TBC Macros and Extensions

Since the TBC crew is unwilling to look into this since literally years, Access is meanwhile able to do it, I'm tinkering on a macro that loads tiles from a WMTS source. 

The TrimbleMaps background seems to be tied directly to HoopsViewCache, sorting everything out automatically. Hence it would just be a matter of Services.TrimbleMaps having the option to set different tile tokens for the URL. Instead of 0,1,2 it'd need to change TileCol, TileRow, TileMatrix. That's so simple that it is unbelievable it isn't possible after so many years.

Currently, there doesn't seem to be a way to tweak Services.TrimbleMaps to download Tiles from anything different than TrimbleMaps, I'm running into errors/dead ends. But it does have some helpers for computing the tile numbers.

My own code for retrieving the tiles still needs some tuning but works. And I can add them as OverlayGeoImage.

But the imagery is shown on top of everything else, covering it.

Is there a way to show OverlayGeoImage tiles in the background, behind all drawing entities? Kind of an UnderlayBag.

Is it somehow possible to remove entities from an OverlayBag without resetting/rebuilding it? I can avoid adding tiles that exist already, but I also want to remove tiles that are outside the current view, without erasing and rebuilding and reloading all tiles, while optimizing the bags amount of content.

Or is there another way to add background imagery? I found something like ImageTileNetwork or HoopsCacheView.