The injected current is flat. For single-run convergence, simply going by the Poisson Tolerance is adequate.
If the Poisson solver is not settled, the user should try the following:
Add more cycles if the trend is decreasing.
Reduce the Poisson Solver Tolerance.
Increase the number of particles injected.
Improve the mesh in the injected region.
Consider a quadratic field solution, with perhaps an even lower Poisson Solver Tolerance.