Axisymmetric Hertzian Contact mechanics model

Hi,

I am trying to model a sphere pushing on a surface. To do so, I have created a 2D axisymmetric model with a point load close to the apex of the half-circle; as putting a point load right at the apex which is on the axis of symmetry returns an error message most probably because of the singularity. Anyhow, the model does not work and either the two parts penetrate into each other or strangely get separated from each other (the point load is downward, so moving up is kind of unexpected). I defined the contact pair under the the model's definition and solid mechanics. Does anyone know why this happens? I thought maybe this is a common problem that might root in a simple mistake in defining the contact.

Thanks
Vahid