We actually prefer to be one tier up from the tanks. In our opinion that makes for the best view. Right up next to it you can only see what's right in front of you. We have been seated in the very back tier before, and while it does definitely make for a different experience, it's pretty cool back there, too.
I agree that only 4 max can sit right by the tanks, and that they will definitely let you wait for the table you want otherwise. Sometimes it's a long wait there later in the day as it is, so I would just take what they give me. We really, really like Coral Reef!!