When the test ran for HTTP 1.1 throughput with the default setting the test ran with zero failures and returned a Grade of A.
When changed the Server file size to 1KBytes and reran the test the Report returned a Grade of D yet there were zero Unsuccessful Transactions.
With Default max http test, we have following pass/fail criteria:
So in case the bandwidth fall below 18.34 Gbps the test will have lower grade though it pass successfully.
If higher bandwidth is required then certainly higher should be the Data Size else the throughput will be low.
For 1Kbytes of data to pass, it is required to alter the value in percentage for bandwidth which can be achieved by running the test few times to be certain as how much bandwidth is achieved with this data size.