Convex shapes can be created in incremental sheet forming by supporting the workpiece with the pressure of an active medium. In this paper, a method is presented for creating irregular convex shapes by adjusting the pressure to control the forming forces. At first, the general characteristics of the forming forces in incremental sheet forming with active medium (IFAM) are investigated based on a truncated pyramid and a truncated cone. The findings show that the pressure has to be adapted for each contour of the toolpath to achieve a specific wall angle. However, this strategy cannot be applied for an irregular shape consisting of half a truncated pyramid and half a truncated cone since the forming forces fluctuate over one contour. To enhance the control approach, a data set is subsequently generated by recording the forming forces under the influence of the wall angle. The data analysis reveals a strong correlation between the height difference per contour and the tangential force. Finally, a control concept is proposed to adjust the tangential force and is subsequently validated on the irregular-shaped part. The results prove that irregular shapes require a sophisticated control of the forming forces to increase the geometrical accuracy.