Mike,
I have their original report as part of the NGF study for Lake Jackson. Back then, they used 1/4" but I think they raised it a bit after the Olympia Hills project near SA. 1/2" per hour could still theoretically drain a 12" storm within a day, with some temporary ponding, which is above 100 year storm level even in Houston.
At our recent grand re-opening up in Wichita Falls, we got rained out with 3" of quick rain. While it cancelled the event, they could have been out playing a few hours after the rain, using similar criteria.
If you think 4" tile looks inefficient, I wonder about that new Sandtrapper system, where they propose to drain bunkers with 2" pipe and a siphon system!
Again, with no power, where are you posting from? Your Blackberry?