Thanks for the details.
I have explicitly changed permissions for directories as required.
But the problem I am facing here is nginx reload fails due to permission denied for proxy_temp folder.
I had explicitly changed permissions for this folder so that it could be accesssed by user abc (user with which nginx is running).
However, when buffering happens, I see that the folder permissions are changed to be owned by nginx user. Hence my reload fails due to permissions issues.
Is there something I am missing here? Does nginx remember the user with which it was installed and is that why these folder permissions are changing?