OS X and Click-through

So which app windows (and parts of windows) in OS X accept mouse click-through and which don’t and why don’t they behave consistently? Seems that the scroll bars of all windows accept click-through, which is annoying, as the scrollbar is usually all that’s visible of the window I wish to bring to the front. This means I can’t easily bring the rear window forward without scrolling the document as well (kinda like Windows™ that way.) Other parts of windows ignore the mouse click and just bring it forward. I can’t seem to sort out if there’s any method behind the madness.