Alerts will look like this, however when you look at the alert you will find more than enough space!
[DataProtection Alert] (SERVERNAME) Database 'EXCH-DB14' is low on log volume space.
Below will set the global permanent override to reduce the threshold to 10Gb, changing the version to match my Exchange Version.
Add-GlobalMonitoringOverride -Item Monitor –Identity MailboxSpace\StorageLogicalDriveSpaceMonitor -PropertyName MonitoringThreshold -PropertyValue 10 -ApplyVersion 15.0.1104.5
After the override is added you will need to restart the Exchange Health Service.