warning: pristine-gz cannot reproduce build of ../fteproxy_0.2.13.orig.tar.gz; storing 17% size diff in delta

ran into an inefficiency when importing the fteproxy upstream tarball as below

$ git-import-orig --pristine-tar ../fteproxy_0.2.13.orig.tar.gz
What will be the source package name? [fteproxy]
What is the upstream version? [0.2.13]
gbp:info: Importing '../fteproxy_0.2.13.orig.tar.gz' to branch 'master'...
gbp:info: Source package is fteproxy
gbp:info: Upstream version is 0.2.13
warning: pristine-gz cannot reproduce build of ../fteproxy_0.2.13.orig.tar.gz; storing 17% size diff in delta
(Please consider filing a bug report so the delta size can be improved.)
pristine-tar: committed fteproxy_0.2.13.orig.tar.gz.delta to branch pristine-tar
gbp:info: Successfully imported version 0.2.13 of ../fteproxy_0.2.13.orig.tar.gz
$ md5sum ../fteproxy_0.2.13.orig.tar.gz
334cbf22b663530f5fae6693dd5a7e5d ../fteproxy_0.2.13.orig.tar.gz

pristine-tar is trusty's 1.30