Animate Objects: Where are the stats?

[Nareau]

The 6th level Cleric spell Animate Objects measures its effect in cubic feet. It refers you to the MM for stats for Animated Objects. However, the MM doesn't seem to measure Animate Objects in cubic feet; it uses size categories.
If an average person is 3-4 cubic feet in volume, the cleric can easily animate a medium size object. Can they animate a large object? Even if they can, it seems pretty underpowered for a 6th level spell. For 1 round/level, you can create a creature that gets a +2 or +5 to hit. At 11th level, this probably isn't going to be particularly effective, even if it's made of something really hard (like iron). And what if you do decide to animate water? Water doesn't have a hardness; would your creature?
The spell seems pretty badly designed (although it's a cool idea). Any thoughts on how to handle it would be appreciated.

Spider

 

[(Psi)SeveredHead]

According to the rules for Dragon 302 (eg balance) you should probably get a gargantuan object for your pains.

That may seem underpowered, but casting the spell isn't a full-round action, the creature isn't affected by Magic Circle against Evil, etc etc.

There is no reliable way of determining what size of creature you get. For instance, take a really long chain (Colossal size, low-volume), and don't coil it ... well, you see where this is going.