This might be more of a bug, but I discovered when you place a Wwise Convolution Reverb Effect with a stereo IR in the Actor-Mixer Hierarchy, mono assets stay mono no matter what setting you set on the Wwise Convolution Reverb that's being applied to it. The files are dialogue files that are being localized in a handful of languages, so I can't just import stereo versions. Putting the FX on a bus instead works, but then I can't render the FX like I was hoping (to save CPU). Hope this can get fixed in future updates!
-Blake