Last summer I exported a RCP file and I was able to get it to align perfectly with survey points in a dwg file, which was probably with TBC v5.1. Now with v5.21 it seems RCP export is always scaling to "ground".
In the Point Cloud export for RCP format, there's an option for grid or ground. Previously, if you set it to grid, it would not scale your data. If you set it to ground, it would scale the data to ground (who knows with what parameters). What I'm trying with my project is unscaled data, so I'm leaving it as grid setting in the exporter. Yet referencing the RCP into autocad, the scan gets placed as if it was scaled to ground. My boundary calculations and autocad's background aerial image confirm that. Even if you set the export setting to ground, it gets placed in the same spot in autocad as it does when grid was selected.
In autocad if I set the scaling option in the reference of the RCP to be the combined factor from Ground to Grid, it comes in within 5 feet comparing to autocad's background map. I don't have access to v5.3 until my license gets renewed at the start of next year.