The results are in... and they are inconclusive, for the most part. (See here for a description of what I'm talking about.)
Here's how the different chives did....
Just water 4.5 inches
Short pot #1 6 inches
Tin Spot #3 7.5 inches
Self-watering 8 inches
Short Pot #2 9 inches
Tin Spot #1 9 inches
Tall Pot 9.5 inches
Tin Spot #2 10 inches
Conclusion: soil is better than just water.
Since the tin is probably shorter than the short pot, I'm not sure height makes as much difference as I'd like to think. Considering the variation in soil pots, I'm not even sure I can claim much again just-water.
Ah, well. Perhaps I'll try more garden experiments in the summer.