How are you comparing to 19:9 or 20:9? Those are rarely precise anymore, even though they used to be.
For instance the iPhoneX resolution is 2436×1125, which ratio simplifier takes to;
2436 : 1125 = 812 : 375
And that is certainly NOT exact! Try it yourself… it is 812.7224-something to 375
You would want to check a range of ratios, and be sure to do your divisions as floating point.
If you do integers, 19/9 is gonna be exactly 2, just like 20 / 9
Instead, use 19.0f / 9 and 20.0f / 9
I usually try to handle everything within a smaller “Safe” area with AspectRatioFitter, or else I try to have special layouts for “wider than 2” or “narrower than 0.5” for instance.
Anyway, here’s some more relevant scribblings to handle UI:
Here are some notes on UI Anchoring, Scaling, CanvasScaler, etc: