According to a video by Real Engineering the ISS has a 50x50x0.75 km exclusion zone.
Why Isn't it spherical and why is the "vertical" axis so much smaller?
Screenshot from Don’t Drop your Tools in Space cued at 10:34
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Most of the risk to ISS comes from objects traveling at relatively similar orbital altitudes. Very little will approach ISS from below as objects doing so would in most cases have to originate from within the atmosphere. And approaches from above will also be limited because such objects will end up in the atmosphere after a single pass of ISS.
But objects in similar orbital altitudes will have repeated encounter opportunities if their orbits cross that of the ISS from different inclinations.