How to export a custom collection?

[Synchro]

I'm using Laravel-Excel in a Nova action. I need to export a set of rows from a resource (always all of them, ignoring any current selection), but importantly, it needs to be prefixed with 4 rows of fixed data. I'm attempting to achieve this using FromCollection, as per the docs:

class myExport extends DownloadExcel implements FromCollection
{
    public function collection(): Collection
    {
        return new Collection([
            [1, 2, 3],
            [4, 5, 6]
        ]);
    }
}

However, when I trigger the action, it downloads the data for the selected record(s) in my view in the default format, and the data returned from my collection() method is completely ignored and does not appear at all in the downloaded data.

How can I do a completely custom download of a collection that ignores the current selection?