You don't have to keep switching back and forth between the Abstract Designer screen and the Designer Scripts window. Do everything in the Designer Scripts window. Add your code there and press F5 to see the immediate effect. Then you can adjust your code and F5 again...repeat this cycle until the emulator or device screen is what you want.
Don't use the Abstract Designer screen to judge your component placement even tho they do move when you press F5. Start up an emulator or if you have the actual target device, connect to it via USB or Bluetooth or the Bridge. In the Designer connect to the device from the Tools menu.
You'll find using the new Designer Scripts is a lot faster to develop your screens with compared to B4A 1.8. There is some improvement tweaking Erel can do with this and many have made their suggestions/recommendations. The next version of the Designer Scripts should really be awesome!
There is a bug currently where by if you have code in the lower Designer Scripts window, you must have at least one line of code in the top window. It can be code that gets changed in the lower window (that's how I do it) but as long as it's in the top window, that's all that matters.