Right now, that is a difficult call. As you know, foxes haven't shifted into their meat only diet just yet. Food is everywhere still, persimmons, berries, insects.
I believe I would try something of low volume such as mouse squeaks or small birds. You might even try kitten sounds, most Reds enjoy a good "cat killing" just out of pleasure.
As the winter wears on and times toughen up, sound selection for a calls really expands. I've called some beautiful reds here on the East coast using a loud Aggressive Jack sound on my FoxPro, but times were hard, snow on the ground etc.
FoxPro has a sound out called Red Fox Rally that might spark interest out of curiousity. It's simply a gathering bark or territorial sound. Hope this prompts your thought process. I know you are qualified enough to "get r done" if it is possible. It is just tough still yet.
Sonny