The streaming overlay can't be changed from 1920 x 1080, the idea is to use OBS / xsplit to scale everything down to your resolution.

You should be able to drag the streaming overlay around on your screen. You might have to right click and disable snap-to or always on top. What is important is that any information on the overlay be within the bounds of your monitor. You can have part of it hanging off of your monitor, but any actual data needs to be within viewable bounds.

As for allowing the user to scale the overlay itself, there are no immediate plans to add that feature in. What is more likely is we port over our DirectX overlay tools and upgrade the streaming overlay all together.