multi-site root site trouble

I have a multi-site installation set up at Dreamhost.

All of my sites should store images at /sites/sitename/files with sub-directories under that which one could drill down into.

Two of my three sites work as expected, no problems.

The trouble arises in the site which is the "main site," that is, when I set up my multi-host install at Dreamhost, I did it with the directory for sitename1.org. After testing it and seeing if it worked (honestly I don't think I'd tested IMCE at that point because the site largely 'just worked'...and IMCE had worked on a previous install of the site with the same database and themes on another host in the same situation), I set up two more domains, sitename2.org and sitename3.org all via multi-host.

Sitename2.org and sitename3.org work, no problems.

Sitename1.org has a problem with IMCE however, in which

file system path is

sites/sitename1.org/files

upload directory is "/"

attachments DO upload to the site, no problems

but if I open IMCE, the following happens

/home/.philie/username/sitename1.org/sites/sitename1.org/files (obviously, the internal director although strangely NOT a path I have seen anywhere in ftp or etc.)

is listed as my path instead of

sites/sitename1.org/files

I am able to upload files, but if I select them, nothing happens, the image doesn't appear in the preview, the URL is blank, etc.

I HAVE been able to get this install to sort of work by changing the folder that IMCE points to (I renamed the old files folder, created a new files folder) but when I tried to create subdirectories in that, it broke again, giving me the bad url above. Since then I've tried to fix things but haven't been able to put them right.