Creating a new symlink prompts the user for a filename, which defaults to the current filename. I think it's much more common to create a symlink to a file in another directory, than to create an alias in the current directory.

My suggestion to to default to the full path of the the directory in other panel (if different) + the current filename. If the user intended to only create an alias in the current directory, they can easily delete the path, but if they wanted to create a symlink from the other directory, it's much harder to type that other directory's path.