This situation is very common in copper coins. Compared with today, the ancient manufacturing process is relatively rough, the casting process itself will have defects, and it will also be deformed in circulation, due to various factors.
At the same time, combined with my calligraphy experience, I can distinguish the difference between normal fonts and objective changes. Therefore, this salty flat is not a special calligraphy, but a vertical exaggeration in casting or circulation.