"AccountingMax 20 TB" doubles the actual network load compared to "BandwidthRate 8 MB"
With "BandwidthRate 8 MB" I do observe a load of about 3-4 MByte/sec, whereas "AccountingMax 20 TB" yields to a load of 6-8 MByte/sec and an advertised BW of about 16.41 MB/sec (F1BE15429B3CE696D6807F4D4A58B1BFEC45C822)
Assuming, that "BandwidthRate" is meant just for one direction, I do wonder about the factor of 2.