TPT return code 12 during INSERT - response (6) by ericsun2

I have question to @feinholz regarding the "Data Block Size"1092632 mentioned in the above log:

ODBC_Operator: sending SELECT request
Data Block size: 1092632 Buffers/Block: 17 Data Buffer size: 64272
ODBC_Operator: data retrieval complete
ODBC_Operator: Total Rows Exported: 2922
And mine load script is dealing with 16K bytes wide row, but it only uses 449912. I want to learn which parameters in TPT script will affect the "Data Block Size" and how to tune it in the positive way.
Task(SELECT_2[0008]): checkpoint completed, status = Success
Task(SELECT_2[0012]): checkpoint completed, status = Success
Task(SELECT_2[0010]): checkpoint completed, status = Success
Data Block size: 449912  Buffers/Block: 7  Data Buffer size: 64272
 
Thanks a lot.