If you reading this, most likely you googled, wtf is "Rate limit IP overhead" option in Deluge.

Official definition by Deluge (who can understand that really?):
"If rate_limit_ip_overhead is set to true, the estimated TCP/IP overhead is drained from the rate limiters, to avoid exceeding the limits with the total traffic"

Here is unofficial :
"Rate limit ip overhead means that your total bandwidth will never exceed the limits you set. If it's not enabled, then the limits you set will apply to the actual amount of data downloaded/uploaded and the overhead will use slightly more."

So, basicly... if you dont have any strict bandwidth limits, I suggest you leave this option as not enabled.

Hope that helped.