I had the same problem with the overlapping quick bars and i found some kind of "work around".
The problem seems to be the padding between the cells which doesnt probably scale with the icon size.
What i did now was to move the affected quick bar to some free space and i started adjusting the width, size of icons and padding.
And what happened was that after some tuning i found some settings which resulted in a quick bar about the same width and height as before, but with slightly smaller icons.
This procedure worked quite well for all my guild mates right now, so there's hope it works for you as well
It just takes some time to find the right settings.