```python
import bluemira as bm
import numpy as np
import matplotlib.pyplot as plt
from fenics import *

# Define parameters for the coil and enclosure
coil_radius = 0.05  # meters
coil_current = 1000  # Amperes
enclosure_size = [0.2, 0.2]  # meters

# Create coil and enclosure using bluemira's geometry tools
coil_circle = bm.geometry.Circle(coil_radius)
enclosure_rectangle = bm.geometry.Rectangle(*enclosure_size)

# Set mesh options
mesh_options_coil = {"mesh_size": 0.01}
mesh_options_enclosure = {"mesh_size": 0.02}

# Create components
universe = bm.Space()
enclosure = bm.Component(geometry=enclosure_rectangle, mesh_options=mesh_options_enclosure)
coil = bm.Component(geometry=coil_circle, mesh_options=mesh_options_coil)

# Add components to the universe
universe.add_component(enclosure)
universe.add_component(coil)

# Create mesh and convert it for use in FEniCS
mesh = bm.meshing.create_mesh(universe)
fenics_mesh = bm.meshing.convert_to_fenics_mesh(mesh)

# Instantiate a magnetostatic solver
solver = bm.solvers.MagnetostaticSolver()

# Define the source term for the problem
source_term = Expression("current", degree=1, current=coil_current)

# Plot the source term for visualization
plt.figure()
bm.plotting.plot_function(source_term)
plt.title("Source Term Visualization")
plt.show()

# Solve the magnetostatic problem
solver.solve(fenics_mesh, source_term)

# Calculate the magnetic field
magnetic_field = solver.calculate_magnetic_field()

# Compare the calculated magnetic field with the theoretical value
# along the z-axis and along a radial path at a certain z-offset
z_axis = np.linspace(-0.1, 0.1, 100)
radial_path = np.linspace(0, 0.1, 100)
z_offset = 0.05

# Theoretical magnetic field calculations would be done here
# This is a placeholder for the actual theoretical calculation
# which depends on the specific problem setup
theoretical_magnetic_field_z = np.zeros_like(z_axis)
theoretical_magnetic_field_radial = np.zeros_like(radial_path)

# Plot the differences between calculated and theoretical values
plt.figure()
plt.plot(z_axis, magnetic_field - theoretical_magnetic_field_z)
plt.title("Difference along Z-axis")
plt.show()

plt.figure()
plt.plot(radial_path, magnetic_field - theoretical_magnetic_field_radial)
plt.title("Difference along Radial Path at Z-offset")
plt.show()
```