I think there is very lottle evidence that foxes try to eat cats. Foxes aren't stupid. There are better things to eat that haven't got the teeth cats and fighting ability of cats. Especially feral cats.

But sensible cats might well prefer to steer clear of foxes anyway, and I suspect that's what's happening in your case.

Here's a quote from this page about urban foxes - "Foxes eat fruit, worms, insects, small mammals and scavenged food. There are cases of cats being attacked, although this is extremely rare. Both foxes and cats are active at night and meetings are probably a nightly occurrence - generally the fox is nervous of the cat." (Of course these are English foxes - I'm not sure if yours woudl eb the same species.