Question regarding git fetch

I noticed that git-fetch seems smarter when it is run without a <refspec> argument than when one specifies a branch name. I use a simple setup where a remote central repository is defined when it is cloned the first time (clone -o central ...). This leads to these default parameters:

remote.central.fetch=+refs/heads/*:refs/remotes/central/* branch.master.remote=central branch.master.merge=refs/heads/master

When I use "git fetch central" each branch in central's refs/heads/ is automatically fetched to my refs/remotes/central/ as expected.

What was a little bit surprising to me is that running "git fetch central master" does not update refs/remotes/central/master but simply updates FETCH_HEAD.

I read the manual and I know that updating FETCH_HEAD is the expected default behavior for git-fetch. However, I really like the fact that git fetch (without <refspec>) knows that ANY branch in refs/heads/ corresponds to refs/remotes/central/. Is there a way to change the configuration to have "git fetch central branch" always updating refs/remotes/central/branch whatever the specified branch.

I would prefer not to have to specify the <dst> each time: git fetch central branch:remotes/central/branch

Thank you, Tom