heirloom always appends a region to the end of the bucket name (the bucket_prefix concatinated with the region) see https://github.com/intuit/heirloom/blob/master/lib/heirloom/archive/setuper.rb#L22.  Heirloom download assembles the bucket_prefix, region and name and id to create the correct s3url.  For example

s3://bucket_prefix-region/name/id.tar.gz