Consider above 2 activities which both having Primary and Secondary SLAs. Current time is shown as a Red Line. It is fallen within Secondary SLA of second activity and consider regarding 1st activity, it lies within Primary SLA. 2nd activity is unlikely to be allocated preferring to 1st because the Primary SLA is missed and now the net value is less. When time is moving, value of activity 2 is becoming less and less therefore, there is a tendency to not allocate it at all. To overcome this, you can define the Ageing Factor to secondary SLA (SLA_TYPE_2 here). What it does is, when the current time is later than the SLA start time it will increase the activity net value. If you set it to 1.5 in SLA Types (obviously the value should be greater than 1 to achieve this), value at current time will be multiplied by 1.5 to give the activity net value hence, it will be allocated against 1st activity because now it is higher than the net value given for activity 1 by its primary SLA.