http://content.hccfl.edu/pollock/aun...rtitioning.htm
This is a good link to show how partitioning works and some samples of partition sizes based on use of server / log size and disk size. As a customer, you will always get some standardized sized var partition unless you ask for different.
My first job in technology was back in the late 90s in the dedicated/colocation department as a unix admin for a large host for a number of years. a big part of the job was doing dedicated/managed server installs on Unix machines. They basically gave me a script to follow and had there own procedures. You would have had to ask to get different, usually paid extra for it. But people did it...