Yeah, the new function maps are very confusing, especially when you need to pass parameters. Have you seen the official "Function maps" template? It explains in detail how to do it.
As a workaround you can use a global variable instead of the parameter. Set this variable to Dialog.At(6, 1) before calling the function, and read it inside the function.
To call the function from a script you can try something like this:
runtime.callFunction("MyFunction", runtime.objects.MyArray.getAt(6,1));
And another option, which I should probably not be mentioning, is to use the old Function plugin. It is deprecated, but it's much more flexible and allows to call functions by name and pass any number of parameters.