No - the exact opposite.
Multiple domains each land in their own folder but much of the code is common to all and needs to be pulled from a shared location. Most of the actual pages will be pulled from the common repository but the includes those pages need to reference will often need to be domain specific.
The problem comes with the shared code which needs to be able to redirect the include calls back to the appropriate sub folders within the original domains to see if there is code contained there and only use the generic copy id a specific one can't be found.
http://specific1.com => look in specific1 first and if not found there then get from generic (for both pages and includes)
http://specific2.com => look in specific2 first and if not found there then get from generic
http://specific3.com => look in specific3 first and if not found there then get from generic
http://specific4.com => look in specific4 first and if not found there then get from generic
http://specific5.com => look in specific5 first and if not found there then get from generic
http://generic.com doesn't exist
The first part works - if the main file isn't found then it gets the one from generic. The problem is that if a file that then needs to reference exists in the appropriate specific folder I need it to be retrieved from there and not from the generic folder.
From the testing I have done the generic page PHP has no way of telling which specific domain it is running in and so cannot access the right specific folder to look for the includes there first.
For any PHP code to work properly it would need to be able to retrieve the displayed URL and there does not appear to be any way for it to do that.
all of these identify the WRONG location when the page loaded from generic as they identify generic instead of the correct starting folder (unless the problem is that I am testing locally using folders that are all sub folders of localhost).
It seems more likely that a minor modification to the mod rewrites in the .htaccess would fix it but I have no idea of what that fix would be.
The pages part works - if page 1 is retrieved from generic and there is a link to page 2 that can be found in the appropriate specific folder then it loads the correct page 2 so the HTML recognises which domain the code is running on, it is only the PHP that doesn't.