hey, figured i'd help. the collider size/radius seems fine but you've set it way off in the distance. a typical offset should be between 0-0.2 and you should be able to see the collider sphere somewhere inside or around the head. also, it looks like you're using the UniVRM-1.0 tools, which isn't officially supported in most apps yet, you should stick to the 0.xx components for now.
here's a screenshot of what it looks like for me. the collider sphere is clearly visible in roughly the same position as my character's head. also note that it's the 0.xx version of the script (it doesn't say "VRM10").