Is Incremental Disk Backup Truly Incremental?

I incrementally back up files in folders daily and that is working just fine.

I write this inquiry because I have been attempting to perform periodic disk incremental backups that don’t seem to be incremental. By that I mean that, although I am not adding lots of data to my disk in between the backups, the file size is roughly doubling in size for the first incremental backup, 50% increase for the second incremental backup, and etc. In other words, I appears to be adding a whole base backup into the file, and after about 2-3 backups, the file is too large for my drive and I have to start over again.

I may be setting parameters wrong and seek guidance/correction
Step 1. What to Backup
Backup Type: (radio button “Disk, Partitions and MBR”)/Select Disk 0 (my C: and D: drives)

Step 2: Backup Destination/My Computer tab
I select my SSD drive (F:)/ default name for backup file=Disk_0_inc_disk.cbu

Step 3: Backup Settings
(As far as I know, I am using the Default Settings)

Selections from my log file are attached. If you need more information or for me to recreate something, please let me know.