Do Cover and Concealment Penalties Stack?

For example, let’s say a kobold is hiding at the base of a tree; he is concealed by some low branches. Then, 5 squares away, there is a PC with a ranged weapon attacking the kobold—but between him and the concealed kobold is a large rock, providing the kobold with cover. Do these two stack, creating a total of -4 to the PC’s ranged attack? Or is it just a flat -2?

Page 29 of the Rules Compendium has this to say about penalties:

Penalties are added together, unless they’re from the same named game element.

Pretty cut and dry! Cover and concealment do stack.

For more discussion on this topic, visit the thread I made on EN World.