I see the issue. The ObjectRefGID is the raw value, but in order to extract the frame ID, the plugin also needs the 'firstgid' parameter from the Tileset because the frame number is relative to the tileset being used. IE: frameNumber=TilesetFirstGID-ObjectRefGID.
As the plugin currently stands I think rexrainbow might need to add the retrieval of the Tileset's 'firstgid' parameter in order to extrapolate the frame number. Sorry for getting your hopes up, but hopefully, Rex will pipe up.
In the meantime, Bjorn, the Tiled developer (am I right in assuming you are using Tiled), doesn't recommend using Tile IDs to reference tiles in a tileset because they are 'volatile'. I had to agree with him because I found out in my situation, I could not reset certain tiles to start at 0 within Tiled. For example, in one of my tilesets, the first tile's id is 3, and there are some the skipped a number. And so referencing them in C2 was yielding incorrect frames even though the tile ordering was identical.
The only practical solution for me was to apply a custom property to each individual tile assigning them a frame number. I think this a much better solution as it is predictable. Also, it is also possible to parse the TMX externally that will procedurally make the correspondence between the TMX tileset and the animation frames in C2.
Lastly, I have modified Rex's code specifically for this 'Image Object Tile ID' requirement, but I have not requested Rex to 'pull' my modifications as I think it's better for Rex to maintain his plugins. If Rex allows me to post modifications to his code then I'll do that here.
But again, I personally have abandoned the idea of using Tile IDs for frame numbers mainly because they're not dependable.