The best way to avoid the problem would be to locate the butted zone and go a few millimeters up from that point. Ideally you'd do this with a gauge of some sort but your stem adjusted so that you can just slide it up and down will also work. The stem will get tight in the steerer when you reach the butted zone at which point you can put some tape on the stem to mark that depth. Don't remove the tape until you've made your final height adjustment and have a gap between the tape and the headset.