As Noknees has said it is most likely the cut of the boot's toe box being too narrow. Possible ways to address this first would be to add an arch support in place of the existing insole. The foot often tends to be slightly more narrow when the arch is fully supported. A thin heel lift under the current insole may also bring the foot back slightly enough where the boot will still fit well and the pinky is then not pressed as much. Another option is too thin out the liner in the toe box area where the pressure is. The less material in that area, the more room you will have. By the way, Burton isn't going forward with their step-in line in the future.