Android Custom Max Aspect Ratio Not Working

I am using unity 2019.2.11
I need our game to run letter boxed at 16:9 on android tablets that are wider than 16:9.
I have tried changing the custom aspect ratio in the unity android player settings to 1.86. These has no effect on wider aspect ratios, they still do not run letter boxed.

If modifying the android manifest XML is the way to do this then I need some clarification on how to do that.

Any help with this would be hugely appreciated.

try to build it and launch, not using remote app. (if you did)
That used to be my prolem, build worked fine, not remote