When two characters are adjacent (one a hovering character, one a grounded character) can you do a ranged combat attack? From what I understand flyers can't make a ranged combat attack out of adjacency while based by a grounded character. But I thought they could still shoot the person basing them, with a ranged combat attack. Is this incorrect?

As of Icons rulebook (pg. 22) a Hovering character cannot shoot out of adjacency but may shoot the figure it is adjacent to.

If you are a hovering figure, you can always make a ranged attack against an adjacent opposing figure, as long as the target figure isn't using Stealth (and you don't have a way to overcome Stealth).

If you are a non-hoverer, you can only make a ranged attack against an adjacent opposing figure is when there are no opposing non-hoverers adjacent to you. So if you were surrounded by hoverers, you could still make a ranged combat attack.

Are you sure that this is still the case? As I understand the Icons rule, an earthbound character can make a ranged attack against an adjacent hovering character even if there are earthbound foes also adjacent. The two rules both appear in the section on flyers, and are worded in a parallel way.

I'm pretty sure (nearly 99.999999%) that it has always been and continues to be the case that grounded characters cannot make ranged attacks when based by another grounded character.

From the Icons Rule Book (page 21):
Every character has a range value printed on its base. This the maximum number of squares that a character’s ranged attack can reach. If the range value is greater than 0 and your character is not adjacent to an opposing character, then your character may make a ranged combat attack. A character can attack in any direction, regardless of the direction it is facing.

And, from page 22:
A hovering character may be the target of a ranged attack by an adjacent non-flying character.

Basically, all the second ruling is saying is that you can occasionally bypass the first no-ranged-combat when based ruling, but only when based by an hovering figure. If based by non-flying figures, the first ruling is still in effect, since there are no other provisons for non-flying figures to ignore the first ruling.

In otherwords, yes, we are sure this is how it works.