git-fast-import yields huge packfile

I'm trying to transform a repository from another VCS into a Git repository using "git fast-import". It appears to work, but the resulting Git repository is huge relative to the original - 18 times larger. Most of the space seems to be taken up by a single large packfile. That packfile is about 967 MB which is about 1/4th the total uncompressed size of all 41785 distinct Blobs in the original repository. The source VCS is able to compress this down to 52 MB by comparison.

Maybe I'm doing something wrong with the fast-import stream that is defeating Git's attempts at delta compression....

Are there any utility programs available for analyzing packfiles so that I try to figure out where the inefficiencies are cropping up, so that I can try to address them?

Anybody have any suggestions on what I should be looking for?

If anyone would care to see this oversized packfile and perhaps offer suggestions on how I can make it more space-efficient, it can be cloned from https://github.com/drhsqlite/fossil-mirror.git - at least for now - surely I will delete that repo and regenerate it once I figure out this problem.