I just tried that (mono cue, with SPATIALIZATION HRTF enabled) and it seems quite good compared to when I use the default. Determining if a sound is behind is quite hard though.
I tried this with my Bowers & Wilkins headphones and cheap super market ones. Actually preferred my cheap ones.
I have the feeling it’s somewhat of an art to tweak well.
Hopefully someone from Epic can share their experience using this 