A surgical instrument includes an ultrasonic transducer, a distally extending shaft, and an end effector at a distal end of the shaft. The end effector includes an ultrasonic blade and a clamp arm. The ultrasonic blade includes an upper treatment side, a lower treatment side, a first lateral side, and a second lateral side. The clamp arm is movable relative to the ultrasonic blade for clamping tissue therebetween, and it provides an RF electrode operable to seal tissue with RF energy. The RF electrode includes first and second electrode side portions. The first electrode side portion is spaced laterally outward from the first lateral side of the ultrasonic blade by a first lateral gap distance. The second electrode side portion spaced from the first electrode side portion and is spaced laterally outward from the second lateral side of the ultrasonic blade by a second lateral gap distance.
