Yes, mID field is properly populated and value is passing, proved this out by calling it in the body of the results page.
Used the session variable to populate it and called the form value in the parameter simply because I was more familiar with the syntax to do it that way.
The call to field 'nothing' is irrelevant. When you use the built in Update Record tool it insists on two fields (One primary and one to be updated), however, it is not referred to in my update statement. Deleted it though and there is no difference.
Yes, form uses POST.