Select the signal type of the sidechain signal as the profile for pure:unmask. The plug-in can then focus the unmasking on frequency regions that are most relevant for this signal type.
For example, if the sidechain signal is a kick, pure:unmask will put a high priority on unmasking the low end and if the sidechain signal is a vocal track, pure:unmask will create space in frequency regions that are critical for a clean vocal sound.