Visual items appear in the same location within trial

[jwright8]

I have trials with three sounds playing. With the first two sounds I have a + appear and a X appear with the last sound. These appear just for the sound and then disappear using duration and delay. The problem is that the +s and X do not appear in the same location even though I use "vertical_center" for the trial template or "alignment": center for the stimuli. If I do these the first + appears on the left, the second in the center, and the X on the right. Here is the code:
    "PracticeTrials": {
    "type": "AFC",
    "stimuli": [["dental_CV1", "Plus_Sign1_dental", "alveo_CV2", "Plus_Sign2_alveo", "dental_CV3", "X_Sign_dental_alveo_dental"]],
    "responses": ["First"],
    "vertical_center": true
    }

I have also tried using "which" and "location". This puts them in the center, but the first + is higher with the second + a little lower and the X lower.
  "PracticeTrials": {
    "type": "AFC",
    "stimuli": [{"which": ["dental_CV1", "Plus_Sign1_dental", "alveo_CV2", "Plus_Sign2_alveo", "dental_CV3", "X_Sign_dental_alveo_dental"], "location": [2,2,2,2,2,2]}],
    "responses": ["First"]
    }

I simply need each one to appear in the same location after the previous one disappears. How do I do that?