There are two possible alarms - volume almost full, and volume full. You can specify what percentage triggers each alarm (globally, and per volume). I believe the defaults are 80% and 95%, respectively. So if your alert at 95% was volume full, DFM can continue to alert for that condition, but won't send a new alert at 96%. You can set your "almost full" threshhold at 95%, and "full" to 99%, or whatever numbers better suit you.
If you want an alert at 95%, another alert at 96%, etc., the only way I know to do it is use an external monitoring tool (like Nagios).
Does that help?