Sure, I'll try. Though the author makes it really clear in the game. (and the game itself rocks, I reccomend looking for the back issue, try the Paizio site)
Basically, if the PCs spend the whole game hiding, and avoiding trouble, they get as little as 0 xp.
If they step up, look for trouble, and save the day, they can get as much as 5,000 xp.
If they step up, look for trouble, and fail miserably, they can get as much as 5,000 xp.
Basically, it treats XP as if the X stood for experience.

An experience being anything the character learns from and lives through, good or bad (or both).
Kind of a Nietzche thang.
In my games, I like the pace of the characters going up one level every game for the early levels, and then after 5th or 6th level, they go up a level every 2-3 games. My players seem to enjoy this pace as well, and so I try to scale the XP accordingly. Of course, I still give out extra XP for a game well played, but mostly, I use the "guidelines" above.
Note: Before anyone "corrects" me, I understand that this system places a lot of power and responsibility in the hands of the GM, and requires a lot of trust between players and GM, and would not work for many groups. But it works for ours!
So, good luck to you in finding what works for you.