Stuck with file backup logic undestanding

Hello to everyone.

Could someone explain to me the logic of URBackup file backups please?

Suggest i have to backup disk D on Windows that contains 20Gb of data and encreasing every day by + 1Gb. I thought that full file backup should be 20Gb and incremental backups should be 1Gb each or so.
But in URBackup there is another picture:

Why it is so?

Then i thought that all the incremental backup are dependent to each other and to full backup, thus if i delete full file backup, incrementals woudn’t work. But in URBackup i can delete anyone i want and other will work, why so?

Third thing i thought that in backups there is always full file backup, but i dont see one in my case:

Please explain to me what i’m doing wrong?

TY in advance.