Questions about New UI in 5 beta9

Hi,

I just install Unity 5.0b9 for current project and start to using new UI system, after a few hours try, I still have some problem to fix.

1, object collder for alpha click
I have some big Image picture take a big part of the screen, but most of it is alpha 0, I also have lots of UI in alpha zone, how can I keep the event not block on it, so I change the big Image object to the first of Canvas child, but run with this, the second problem come, is there a way to work with alpha click or polygon collider?

2, UI depth/order
I think it should be keep same order what Hierarchy show up, but after press play, one of the object render last automatic move up in Hierarchy, can anyone explain why it happen?