Now it is looks to whole koji history for given package. It gives not bad results, but it makes more sense to use some sliding window (e.g. last six months).
PR #2421
Metadata Update from @tkopecek: - Custom field Size adjusted to None
Metadata Update from @jcupova: - Issue tagged with: testing-ready
Metadata Update from @jcupova: - Issue tagged with: testing-done
Commit df126222 fixes this issue
Commit a753d280 fixes this issue
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/koji/issues/2420
Please continue any further discussion there.