I have triple checked that the plugin is up-to-date and the constants are all correct.
No sense in configuring the plugin dozens of times instead of once per multisite. The core function of the plugin still works.
It’s just specifically the Email Test feature that is broken when I configure it this way. I can just test a different way, but this is definitely an issue that persists again and again across several different WordPress Multisite installs.
Just letting you know that I’ve done the testing and this bug does exist.