You can find options for the project-wide appearance and position of chord diagrams on the Chord Diagrams page in Engraving Options.
The options on the Chord Diagrams page in Engraving Options allow you to change the default number of frets shown in chord diagrams, the scale factor of chord diagrams relative to chord symbols, and the precise dimensions of each aspect within chord diagrams, including the thickness of strings and lines and size of dots.
You can also change the appearance and position of fret numbers, such as showing them as Roman numerals.
The options are accompanied by diagrams to help you visualize how they affect the appearance of your music.