Don't ball to begin with. What you are experiencing is nodules. This can do with tungsten contamination from the metal, or with tungsten quality itself, even grinding angle and grind quality. The difference in Amperage is that the meter is calibrated to Advanced Square wave. Since the wave form is different, it reads differently even though it does reach the same level. The shape of the wave form of each is actually cooler because less time is spent at the max part of the sine wave.