Good Day,
Start by looking at this
Anchors
Then, get to know your design screen
1. Your selected control. Note the white dots - they correspond to #2.
2. Set your Anchors here
3. When you have designed your screen - send to the UI Cloud for a Quick check
4. Your Scripting Area
X = Horizontal
Y= Vertical
(until you flip the screen)
Note Top Right - Use Check Anchors to make sure you have done it right.
If your devices is connected (F2 - bottom left will tell you if you are connected or not) , then you can connect to that to see in real time what your design looks like
After using "F6" Send to UI Cloud, you get this in your browser
You can immediately see that you have a problem with the Nexus 5x 5" screen. This implies that you might need to add a derivative to counter this problem.
Try to avoid using many derivatives as this become hard to maintain and cause a lot of overhead.
What I sometimes do is create 2x derivatives just for a tablet (800 x 1280) or (1280 x 800) - although this I do not do often as I do not write much for tablets.
I trust this will go some way to clear up your problem.