Wwise manual states - “With 4.x and 5.x configurations, there is only one pair of speakers that is not in the front, so there is no distinction between "side" or "back" channels.”
This generalisation is not always helpful as many 4.x and 5.x configurations have rear speakers at 110-120 degree angles at the back of the listener. When 4.x and 5.x multichannel files are played back on a 7.x or 9.x system, sounds that should be positioned in the rear of 5.x systems end up being the SL and SR channels (commonly referred to as Lss and Rss channels in 7.x and 9.x configurations)
If an ambience file was created in 4.0, playback would be restricted to L/R/Lss/Rss in 7.x and 9.x using the current configuration and mapping. Is there any way to change this default mapping so Ls and Rs channels are mapped to Lsr and Rsr respectively?