firstly, its not an exploit. It's you capping your upload and thusly your upstream doesn't affect your downstream. That accounts for a tiny speed increase, yet your overall session credits remain unaffected.
Secondly, just like emule, the bandwidth reported is inaccurate. Use a network connection monitoring tool to see accurate results.
Thirdly, what's the point in trying to leech, its people with that attitude that ruin p2p programs

I hope you are sharing a fair amount, by the sounds of it you are only wishing to 'exploit' it to leech