We understand this can be annoying when designing a presentation. Our designers have a couple of workarounds you could try.
You can move topics on the overview towards the border so that it adjusts, then click on Background > Adjust background to overview. Afterwards, the image gets bigger and you can move the topics back so that the border readjust itself.
You can also make the edge of the image a bit blurry so it isn’t that distracting when you zoom closer if you open a topic near the edge.
Another method can be to set the background image black so it would fit more into the environment of the monitor or screen where the presentation will be projected.
I hope it helps!