Snapshot Pro Destination Customization

I'm getting started using Snapshot Pro to backup my multisite network. I have configured the local folder under Settings to C:\Snapshots\

I have created three snapshots (one for my root admin site, and one for each of two client sites in my network). In each snapshot settings, I have tried different settings in "Directory (Optional)", attempting to make each site store its snapshots in a subdirectory of C:\Snapshots\ but none are working.

Root Snapshot Optional Directory = [DEST_PATH]/[SITE_DOMAIN]
Client 1 Snapshot Optional Directory = /[DEST_PATH]/[SITE_DOMAIN]
Client 2 Snapshot Optional Directory = [DEST_PATH]/[SITE_DOMAIN]/

Regardless of what I put in the Optional Directory field, all 3 snapshots were created as .ZIP files in C:\Snapshots\ without creating any subdirectories.

Am I doing something wrong?