I think I've found the holy grail usage for APU Loudness Compressor in my workflow. Once I am satisfied with the mix I render the vocals at -24 Lufs and the Instrumental at -24 lufs. Then I place APU Loudness Compressor on each using the ranges shown in the attached pic. The setup is providing expansion on both stems, but I set the range for the vocal with more headroom. This is locking the vocal upfront without a ton of micro managing and without compression. I can see myself using the same combo on kick/bass. More experimentation to be done but so far I'm real happy with the results.

Love this!

I am wondering if I'm just adding volume as the expansion doesn't seem to be dynamic, at least at the limited range I'm defining. Probably overthinking it at this point as it just seems to work. At least so far.

Edit: Looks like I needed to update the compressor after having updated Reaper recently. Everything working as it should now with the expansion being dynamic.

something happened in one of the recent updates and the little gain meter on the far right is gone? is there a way to get that visual feedback, back?

oops! Fix is on the way..

Fix is up fyi, thank you for letting me know!

I'm still kicking on this thing.

Fixed an issue where auto-range wasn't working properly while thresholds are disabled.

Set the alternate dynamic types to always show the transfer function automatically. Should've always been that way probably.

Also fixed an issue where sidechain signal was being used to drive the built-in limiter. Which doesn't make sense! You'd get overshoots when the limiter and sidechain were both enabled. That's fixed now.

Have another sidechain fix on the way tonight -- Bypass and Gate modes will use the non-sidechain signal during gate/bypass. In other words, when the sidechain signal is below source min, it passes through the non-sidechain signal. I think it's much more practical in real world scenarios this way.