SAB does an adequate job (most of the time) of making things easy for the developer, automagically breaking up the border and, quite amazingly, finding the blank area in the middle where the text goes. But it doesn’t always get thing right, sometimes skewing the border in odd ways or making margins inconsistent.
I’m not proposing the current ability be removed.
But I think there should be an advanced feature, where the developer can give the individual pieces and SAB builds the border for each phone. (PTXprint builds borders this way).
Probably only 3 pieces are necessary, F=corner, T=Top, S=Side. Once you’ve input those 3 images, and told SAB what width you want the border (probably as a percentage of screen width), then it would fit the pieces to your aspect ratio:
(Technically maybe even top and side could be the same, just rotated, but I’ve seen some borders where that wouldn’t work).