Sorry. My eyes just slid right past those lines, I guess.

Try:
    Range("L2").FormulaR1C1 = _
        "=SUMIF(R[1]C[-11]:R" & BottomRow & "C1,RC[-11],R[1]C[-1]:R" & BottomRow & "C11)"
    Range("L2").AutoFill Destination:=Range("L2:L" & BottomRow)
As for moving the border at the bottom, the code I supplied should automatically reference the bottom row. If you need it somewhere else, let me know where.