problem with wordpress running on subdomain

I just transferred to a new host. My old host had a directory structure that seemed to be a bit easier to deal with. The main was in a <user>\www\ folder and the subs were in a <user>\<subname>\www\ folder. This was much more conducive to redirecting users from maindomain.com/subname to subname.maindomain.com by simply creating a folder in the maindomain’s root like <user>\www\<subname>\ and dropping an index with a redirect to the sub. My new host has the subs right off the main so it would be <user>\www\ for the main and <user>\www\<subname>\ for the sub.

I’d like a user who points their browser to https://www.maindomain.com/<subname>/ to be redirected to <subname>.maindomain.com but I’m not sure how to make this happen. I’ve got separate wordpress blogs running on the main and on some of the subs. If I point the browser to a sub that doesn’t have wordpress (just a regular html file) it loads it as if it were a page in a subdirectory of the main site. But if I try to do the same with a sub running wordpress, I either get a 404 error from the server, a 404 error from the subs install of wordpress, or it redirects me out to the front of the main site.

Is this a wordpress configuration issue or is this something with which I need to ask my host for assistance? Incidentally, it has the same problem with subs running other php based systems (like mediawiki) so I wonder if this could be solved by a .htaccess or what. Thanks for your help!