A magnetic data storage system according to one embodiment includes a magnetic head adapted to record data according to a shingled magnetic recording (SMR) process. The magnetic head includes a main pole adapted to produce a writing magnetic field, a trailing shield positioned above a trailing side of the main pole, wherein a trailing gap is defined between the trailing shield and the main pole, and a spin torque oscillator (STO) positioned above a first trailing corner of the main pole at an STO-side of the main pole, wherein the trailing gap has a greater length in a film thickness direction near the STO-side of the main pole and a lesser length in the film thickness direction near a second trailing corner of the main pole opposite the first trailing corner in a track width direction of the main pole.