ok, you want to limit.
what prevent leeching does is to limit to "1" the number of connection on the same file.
all those connections will disappear.
Now I can limit the download connection but for "sending connection" I can't.
There's no difference in this case: if those "sending"s are issued by the download manager as you say, then HFS is considering them as "download"s.
This if you didn't mark them by using the "don't consider as download".