If your servo plug is indexing fine, orient the ESC plug the same direction then. Different receivers are wired differently, and I don't know what your using; but if your servo plug fits fine that should orient right, make the ESC plug in the same direction.
..and shaving off that tab is what probably 90% of us do.
What matters is that the plugs are orienting where they should, you should have some documentation that tells you which way the white, red, and black should orient.
Also...If the smaller two wire battery plug to the receiver from the ESC indexes into the receiver, use that as reference of where your positive and negative wires should be plugging into from the ESC and Servo; the white wire (signal wire) will be the obvious choice then.