If you're talking about how much of a packet the CSS will look at to match a URL, it is actually based on how many packets

(config) spanning-packets

From Command refrence:

"In some environments, URL, cookie strings, or HTTP header information can span over multiple packets. In these environments, the CSS can parse multiple packets for Layer 5 information before making load-balancing decisions. Through the global configuration mode spanning-packets command, the CSS can parse a maximum of 20 packets with a default of 6.

The CSS makes the load-balancing decision as soon as it finds a match and does not require parsing of all of the configured number of spanned packets. Because parsing multiple packets does impose a longer delay in connection, performance can be impacted by longer strings that span mulitple packets. "

Thanks

Syed Iftekhar Ahmed