Thanks! As a datapoint, the order of magnitude [10km -100km] range seems like the focus of his recommendation:
More and more States are developing their own domestic space launch capability. Few of these new space powers will be able to freely access space, or utilize the most efficient launch azimuths, if neighboring States can claim
sovereignty up to even 62 miles (100 km). They will have even more difficulty returning objects to Earth if the boundary is set at that altitude. Even the U.S. and
Russia are facing limitations on their ability to freely access space. Setting a low vertical limit on State sovereignty will ensure all States have equal access to
space. (p81).
More and more States are developing their own domestic space launch capability. Few of these new space powers will be able to freely access space, or utilize the most efficient launch azimuths, if neighboring States can claim sovereignty up to even 62 miles (100 km). They will have even more difficulty returning objects to Earth if the boundary is set at that altitude. Even the U.S. and Russia are facing limitations on their ability to freely access space. Setting a low vertical limit on State sovereignty will ensure all States have equal access to space. (p81).