I was told there are a number of things that determine your IPC - previous military experience/rank; previous work experience and degrees. I was given an IPC even higher than 2 because of my time in/previous rank in the CF (with the reserves); my civilian work experience and my 2 degrees that are directly relevent to the my chosen occupation (B.Comm & MBA). In my case I was told the biggest factor was my rank leaving the reserves (as they've recently changed some rules making it more enticing for reservists not to lose pay levels when they go to the regs) and my master's degree (which I'm told automatically bumps up an IPC 2 or 3 levels).
I think their goal is to look at someone's qualifications (education, previous experience, etc) and say - if this person were to walk into a federal gov't job right now, what level would they be entering at - from a junior to intermediate manager. If someone is entering right out of university, then it would probably be junior, if someone is entering with a few years of relevent experience in the private sector, it would be higher. They have been working the Quality of Life Program over the past 8+ years for NCM/Officers in the CF to have a pay system matched better with the public service.
Hope that helps. Are you going on the fall IAP/BOTP course?