tux performance on Linux 2.4.17

Greeting:
Recently I did a simple test trying to compare the performance of TUX
and Zues, Flash, as well as Apache1.3.20. For each test run, all clients
request for a same file. And run this test from small files to large
files.
Very surprising, though the throughputs of small files of TUX do exceed
other servers, for files with size larger than 4K, TUX's number is
almost as low as Apache's.
If I am not wrong, TUX's copy free is set by default. Thus one would
expect to see more benefit for large files. So I am wondering if there's
any configuration tips I missed.

Any idea? Thanks in advance

- Randy