Flying characters get no penalties on ranged attacks
per se, though their elevation might help them avoid some penalties.
As for the tunnel question, it helps if you turn the situation onto its side, putting it on a map. If you're at the mouth of the tunnel, you have a line of sight to everything in the chamber (the red line), but things close to the ceiling will have cover (anything above the green line).
If you step back (the second image), your line of sight is blocked; you can only see what's below the red line. Anything above the green line has cover (if you can see it at all).
PC Jacktucker:
That cover goes both ways. If I can't see them then they couldn't see me. A ceiling blocking my view blocks theirs as well. Correct?
For this, you need to know how you determine line of sight and cover.
SRD:
To determine whether your target has cover from your ranged attack, choose a corner of your square. If any line from this corner to any corner of the target’s square passes through a square or border that blocks line of effect or provides cover, or through a square occupied by a creature, the target has cover (+4 to AC).
When making a melee attack against an adjacent target, your target has cover if any line from your square to the target’s square goes through a wall (including a low wall). When making a melee attack against a target that isn’t adjacent to you (such as with a reach weapon), use the rules for determining cover from ranged attacks.
It's entirely possible for a creature to have cover from your attacks, but be able to attack you without hindrance. For instance, assume that the creature you're attacking is hovering just above the entrance to the tunnel -- on the map I posted, that would be the square where the red and green lines intersect.
Pick any corner of your space, and draw a line to any other corner of the target's. If you can do so without hitting something solid, you have line of sight.
Now, pick any corner of your space, and draw lines to all four corners of the target's square. (For larger targets, you can pick a single square, instead of the entire space.) If any of these four lines hit something solid, the target has cover.
To use the example location (right above the tunnel mouth), you have line of sight to him, but he has cover. If you take one of the bottom corners of the creature's space, you can draw unobstructed lines to your character's space. This means he has cover from you, but you don't have cover from him.
Note (in case this comes up):
1/4 concealment = 5% miss chance
1/2 concealment = 10% miss chance
Now in game terms there is some more leeway; the DM may determine at his that a fog is very light so you are only given 10% concealment to near-total darkness which gives 40%.
This message was last edited by the GM at 00:41, Tue 27 Mar 2007.