In preparation for a discussion of intensity-based panning,
a) read the Wikipedia entry on panning,
b) take a look at these three consecutive examples:
Linear amplitude panning
Constant power panning using square root of intensity
Constant power panning using table lookup
and
c) read MSP Panning Tutorial 1: Simple panning.
(The link is to the web version of the documentation; you can also read it in the Max Documentation within the Max application, which will allow you to try out the tutorial patch, as well. If the last part, about “speaker-to-speaker crossfade” makes your brain explode, you can skip that part.)

Take a look at this abstraction for constant-intensity panning, which you might find useful in your own work.