Hi @nadine-rasu
The images size is fluid (%), so if its 100% of 7 columns it will be smaller then 100% of 8 Columns.
The numbers in the grid area are like counting the Grid Lines. the start of the grid edge is 01. So column 1 is Start 01 End 02.
So If you want to position in columns 3-7 you need to define Start 03 End 08.
Hope it makes some sense 
By the way, we are working on refinements for the Grid Area to make it more clear.
Best,
Yanay