The upper part of Ji is written as soil. This writing method is conventional in calligraphy and there is nothing wrong with it.
In terms of etymology, the origin of the word "ji" is knowing, with an upper and lower structure. The upper part represents weapons, and the lower part is a container. Putting weapons in a container to make a truce indicates auspiciousness. The writing method of the prefix "Tu" can be said to be a variant of Chinese characters. In folk custom, the prefix "Tu" is often used. "Tu" refers to the earth, which means good luck.
There are many calligraphy fonts we see now that we are not sure whether they are familiar characters, or even recognize them. That is because calligraphy pays attention to brushwork and shape. In order to look better, calligraphy will change. A stroke or shape.
Extended information:
The evolution of the word Ji:
The word Ji is a knowing word. The part above the character "吉" (Picture A) in Oracle Bone Inscriptions (Picture A1) is originally a simplified form of Picture (A2). Picture (A2) shows the shape of a tall bowl called a bean used to hold food in ancient times, filled with food for ancestors and gods.
As a component of a character, the "口" below the character "吉" meant steps, thrones, altar tables, thresholds, etc. in ancient times.
Judging from the structure of the whole word "吉": putting food filled with "beans" on the altar table means that there is something auspicious for the family. Therefore, the original meaning of the word "吉" is "auspicious".
Picture (B) is still Oracle, but the "beans" and "food" in picture (A1) have been realized into the glyphs of picture (B1). This "ji" character developed to the bronze inscription stage of picture (C), and even changed picture (B1) into the shape of picture (C1).
As a result, Xiaozhuan (Picture D) of the Qin Dynasty and Official Script (Picture E) of the Han Dynasty inherited the form of bronze inscriptions, and later developed into the regular script "吉" (Picture F). Today it is simply written as "吉".
Reference: Baidu Encyclopedia-Ji