@mina I used to test the Fullscreen Scale with "fluid layouts" and with a HUD layer with Parallax 0,0.
Look at my memory game: Crocodile Memory Game
Select Easy/Medium or Hard, in the level the Croco on the right and the Turns/Matches box are in HUD (Parallax:0,0) and this sprites/texts all have an Archor with Left edge: Window right, Top edge: Window top. The Right and Bottom edge is not set!
It works very well on any phones, and screen sizes.
I recommend to use Archor only if requied, use it with Left-Left and Top-top setting, and only if you want to float something to the right, set Left-Right and Top-top setting.
In scale mode do not use any setting for Archor Right/Bottom edge, cause the scale logic will scale it for you!