Hi NK,
Yes, the denominator in that equation is equal to the total data volume for GPRS. For EDGE, the corresponding counters are DLTHP1EGDATA, DLTHP2EGDATA, DLTHP3EGDATA and DLBGEGDATA.
Alternatively, you can use DLINTBGVOL+DLSTRVOL to determine the total data volume downlink, and this includes both GPRS and EDGE.
Regards,
SHELDON