Again thank you for sharing your experience! I´ve just finished some focus testing for 18mm and 23mm focals with a tripod. Testing both, the smaller square focus and the step up bigger square focus.
At 18mm the focus is clearly better with the smaller square. The same at 23mm. And this is with a tripod and still object... shooting with handheld and people... this gets much worse. So I still think we need a smaller square.
Here is the test, there is a quality lose in both ways, but if you can´t see it at 100% size try this: http://1drv.ms/1MsPAmM
Edit: I don´t own the 10-24 anymore, but I tested a few weeks ago and as long as I was going wider with the focal lenght the focus lose got worse, that´s why I gave it back. (Fuji please... smaller points )
Regards!