sounds like your set-up is fine, and you are seeing the results of many computers all participating in getting that file shared

if many hosts are sharing a file (or a piece of it), LW will download from the fastest hosts that have the next piece you request.

So, looks like many are asking for pieces, and a slow host has the whole file. When one of the other fast hosts gets a piece, they share it and your dl jumps.

If you have tooltips turned on, hover the pointer over the file name and see how the hosts are behaving.