It gets even more fun
The Sage has ruled that if a Ray spell misses its target - even if it goes on to strike something beyond that target - the Ray has no effect.
For example, if Fred the Fighter was standing in front of a door, and Wally the Wizard cast Disintegrate at him, only missing because of Bob's Dodge bonus, the Ray is presumably going to hit the door (or at least the wall)... but nothing is Disintegrated.
However, if the Ray misses the target because it strikes intervening Cover, it affects the Cover normally. So if Clem the Cleric was standing between Wally and Fred, providing half-cover, and Wally rolls in that unfortunate zone where he misses due to the Cover bonus, Clem gets Zapped.
Now. If someone is behind a tower shield, they have full cover... except against targetted spells. And the FAQ has ruled that this includes Rays. So if Fred is hiding behind his tower shield, Wally just needs to Zap the face of the shield to Disintegrate Fred (incidentally leaving the shield unharmed).
But what if it's not Fred with the shield, but Clem? Fred presumably gets at least some cover bonus for being behind a person who is cowering behind a tower shield.
If the Ray strikes Clem's shield, does the shield get Disintegrated, or the Cleric? In the previous example, the shield was being used to target the wielder. In this case, the shield-wielder is not the target at all... is the shield now treated as an object which is providing cover, or a possession of a person who is providing cover?
-Hyp.