What is the formula for experience points gained for killing monsters?

I've noticed that I don't gain any experience anymore for certain kinds of monsters, at least there appears no entry in the combat journal. I suspect that the XP formula is level-dependent, so that you don't gain any XP anymore for monsters far below your own level.

Is there anything known about how the experience point system works in the Witcher 2?

From what I've seen and found from other discussions:

You get less or more experience depending on the level difference(which makes the game more challenging).

Experience gain is limited by mob type or area(to prevent extreme farming...or as protection, because it's possible in games that due to some bug you get imbalanced experience over and over).

Max level by chapters, I'm not sure abut this, but when you go to complete quest and gain no experience it could be this(makes the game challenging and protects from farming).

Level 35 max level in game(useful for planning skills).

And lastly the plain old bugs that occur in every RPG that tries to give you more freedom.