Behavior at Axis of Symmetry

I am simulating a 25 nm radius gold wire in a dielectric cladding. I am measuring the characteristic impedance of the mode of the wire. I have run it in both 2-D axisymmetric and in eigenmode analysis.

My question is regarding the behavior at the axis of symmetry in the axisymmetric mode. The plot should be constant inside and outside the wire, and the expected plot is shown in the eigenmode simulation. However, in the 2-d axisymmetric, I see change in the value at r = 0. Does anyone know why this occurs and how I can avoid it/if it is avoidable?

I am attaching the COMSOL simulation files and powerpoint of the plots I am talking about.

Best,
Cheng-Ming