The point I'm trying to make is that I didn't know that was the default. Neither did I know it existed or was set or was defined. (I assume it's a valid format?)

I tried to declaring it with $^ it didn't help.

I don't understand. If you didn't populate the parameter, of course you won't see a header. Was a compilation error produced? If so, what was it?

The minimum program just involving the format definitions, the setting of parameters, etc. (as well as use strict and use warnings) will give you a proof of concept, an easier situation to debug.