I am the Kat that Walks By Itself

In my experience, the naming thing depends on so many external factors that learning the rules can take forever. My experiences

Honorific Surname implies either formality or distancing (possibly with emphasis on the difference in social standing between the sddresser and the addressee)

Surname alone implies somewhat less formality, or can be a shorthand once the Honorific Surname form has ben used at least once in reference to that person. I see it very much as a carry-over from public school and or the military when used in conversation as opposed to news reports

First Name (Middle Name) Surname is generally used either when confirming the identity of a person (Hermione Granger? I haven't seen you in years! You've certainly changed since Hogwarts!) or a more extreme form of distancing/expressing displeasure (Hermione Jane Granger! How could you turn Draco Malfoy into a cocker spaniel!

First Name alone definitely implies informality, although it's becoming quite common to use it in emails even to quite important business contacts (I'll still use a more formal version when requesting someting that has the potential to be refused, though)

Does any of that help?