Hydraulic gradient near the wall

Hi all,

When performing seepage analysis and get the hydraulic gradients from the Plaxis 2D (purpose to calculate the factor of safety against piping or boiling effect manually), the gradient near the wall is greater than place close to it as shown below which is not possible. Why it comes like this?

    => here 2m head difference and number of equipotential drops is 10 which will give head drop in each zone as 0.2m

Thanks.