Here is the text tip from utstats for EFF:

The formula is easiest to understand if you reduce it to: EFF = Kills / (Kills+Deaths)
If you don't die and make at least 1 kill you get EFF = 100%
Because of the zeroping mod it isn't unreasonable to shoot well with a 300 ping. It matters more that your ping is steady. With primary fire anyway, you hit where your crosshair is when you shoot.
The bots on the London server are set to be pretty easy as they are meant mostly for target practice until other players show up. It also helps if you are a long distance shooter and have your fov set to 80 on that map 😉