The good news is that you can throw away the SUMPRODUCT function and replace it with a pair of COUNTIFS functions. The COUNTIFS can use full column references without detriment and is vastly more efficient than the SUMPRODUCT even with the SUMPRODUCT cell ranges limited to the extents of the data.
In N2 as a standard function,
=COUNTIFS(B:B, B2,M:M, "<"&M2)+COUNTIFS(B$2:B2, B2, M$2:M2, M2)
Fill down as necessary.