P Rating in 2nd edition

I haven't had a chance to read the entire book yet so I may be missing something, but I can't see how PCs raise their P-Rating about 6 (2d4-2) on a permanent basis. Is this intentional or are there things I haven't gotten to yet?
If you start with the telepath class, you can swap your first Telepath feat for a +6 to your P-rating.