Jeff,
When you enabled the events, you must have configured some thresholds. Check the WIPS Events --> Excessive tab. The Event is triggered when the sensor finds a certain number of probe requests within a certain time interval (say Y). Both these fields are configurable and the default number is 30 scans for one client. So if you configure the time interval (Y) to 1 minute, then it is easy to trigger the event.
Please check what values are configured. For these events, you can configure thresholds depending upon how aggressive detection you want.
regards,
Sukhdeep