In 6.3.1 this can be modified to suit your needs on when an event fires into a logfile that is watched with Manager Monitor. The logic is when the event gets fired from the system which you can configure in the cmc. The percentage is not listed in that rule. The != parts are intended to stop a false positive that happened in the past.
Go to the section "Create a disk usage warning when reaching certain set values" in LEM 6.3.1 Release Notes - SolarWinds Worldwide, LLC. Help and Support