CST contour plot problem, same point give different values at different view

I am doing some simulation for a coplanar waveguide. After CST finished the calculation, I use the plot tool in CST to give me contour plot of the Abs value of the H field. To my surprise, if I plot field on the z=10 plane the plot shows the field range is from 200-1500A/m, but if I plot on the y=0 plane the field is from 300-3000A/m. Since the two plane have a intersection line, I use mice to pick the field for a same point, it gives me different values for the above different cases, which mean in the programe the field at same point is different if you look from different directions.
I am really confused now.