The Symantec proxy server's ICAP Service settings provides a button called "Sense Settings" to get the settings from the Network Prevent for Web server in request mode. The settings information determines the "Maximum number of connections" value for the ICAP service and you want to know how is this value determined or set in the Network Prevent server?
The Advanced Server settings on the Network Prevent server has an option to set the number of connections that it is able to communicate with which is called Icap.LoadBalanceFactor. When this value is set to 1 that means that there is only one connection to this Network Prevent server and the value in the Symantec proxy server's ICAP Service settings will show the "Maximum number of connections" equal to 128. So if the value is less say for example 32, then this means that the Icap.LoadBalanceFactor has been set to 4, thereby it the connection is split into 4 for 4 proxy servers i.e. (4 * 32 = 128).