Why won't Excel recognize this pattern as I drag it down the column with Autofill?

L26 cell has =SUM(Sheet1!$C1:$BB7)
L27 cell has =SUM(Sheet1!$C8:$BB14)
L28 cell has =SUM(Sheet1!$C15:$BB21)

But when I highlight these cells and click Autofill in the bottom right, it returns this in cell L29:

L29 cell returns =SUM(Sheet1!$C4:$BB10)

Any help would be greatly appreciated.

Thanks in advance.