So I get when talking about a full scale you want to use all the letter names for the notes (like C# you'd say is C# D# E# F# etc)... But if I were to ask you what the 3rd of C# major is, would you still actually say E# instead of F? Like if you were playing in a band and there was a song in C#maj and the guitar player or sax player or whoever asked you "hey, what note should I play here?" Would you ever respond by saying "E sharp"?
in regular conversation you can use what i call the "reasonability rule" which in this case would be to call it F