Hi,
What is "Slot Allocation" in the Connection Preferences window ?
Example :
If you set max upload to 12kB/s :
Setting slot allocation to 2kB/s give you 6 upload slots at 2kB/s each.
Setting slot allocation to 3kB/s give you 4 upload slots at 3kB/s each.
Setting slot allocation to 4kB/s give you 3 upload slots at 4kB/s each.
A++