There is a similar idea already, but my point is to also make the customization of the trigger area width possible.
I have a S9+ with curved screen edges and which makes it harder to open the menu. Probably as well because of an option that's ment to block unintended touch inputs, I guess especially at the edges which is useful in general.
Also phone cases that go far around the egdes make it more difficult to open the menu quickly and conveniently. Same if the margin between skin and phone frame is very slim, your finger always hits the edge of the phone body before the edge of the screen and may miss the second one then.