The reason that you might be seeing the Peak traffic is higher than the max partition size was because partitions do not calculate and account for SYN packets, therefore if a large number of SYNs is seen for this class, it could cause a partition burst over its allowed limit. 

However, if you would like for the SYN packets to be enforced by the partition size, you can issue the command " sys set tcpSynControl 1 ".
This is a system setting variable that basically enforces the SYNs to be included in the partition calculation and preventing the partition from bursting over it's configured limit.

An example as shown below:

PacketShaper# sys set tcpSynControl 1

Warning: This system command may impact the unit's operation.
        Modifying its default value or setting should be done only
        under the guidance of Packeteer Customer Support.

PacketShaper# sys set tcpSynControl

System values                   Current   Default   Min       Max
=========================================================================
tcpSynControl                   1         0         0         1

Warning: This system command may impact the unit's operation.
        Modifying its default value or setting should be done only
        under the guidance of Packeteer Customer Support.