There is no limit in calligraphy. Rules in calligraphy are the starting point. Once you master them you can break them, but you cannot break something you cannot see or touch.
When you look at a writing of thuluth script, you will notice invisible lines going in a certain angle that have measurements, like 5 dots or 10 dots. Zakariya hoca said, “these relationships of dimensions are only the beginning of writing.” Therefore, when you are first learning how to write in Arabic calligraphy, you are learning the measurements of letters.