Hello, for fountain pens, the large pen tip you refer to is an "art pen", while the small pen tip is the ordinary pen we use. Artistic pens, also called calligraphy pens, are specially designed for calligraphy enthusiasts. However, this does not mean that ordinary people (non-calligraphy enthusiasts) cannot use artistic pens, nor does it mean that ordinary fountain pens cannot be used to write calligraphy works. The characteristic of the art pen is that the tip of the art pen is curved upward. The strokes of the art pen at the same angle are thicker and the lines change obviously. It can reflect the unique frame structure and line changes of calligraphy, especially when writing official script. Therefore, for most people, the writing effect of using a craft pen is better. But I personally often use ordinary pens when practicing calligraphy, so I suggest you give it a try too, just to have some fun.
Thank you!