Circles in matplotlib overlapping when they should not

I am trying to plot two circles in python using matplotlib. I chose their positions such that they should not overlap. However, in the plot it looks like they do. Can anyone tell me where my mistake is?

    import numpy as np
    import matplotlib.pyplot as plt
    plt.rcParams['figure.dpi'] = 5000

    radius = 0.0025
    positions = np.array([[0.5, 0.05], [0.5 + 2*radius + 0.001, 0.05]])

    fig, ax = plt.subplots()
    ax.cla() 
    ax.set_xlim((0, 1.0))
    ax.set_ylim((0, 0.1))
    ax.set_aspect('equal')
    for n in range(len(positions)):
        circle = plt.Circle((positions[n, 0], positions[n, 1]), radius=radius,                              color='r')
        ax.add_patch(circle)
    plt.show()
    fig.savefig("circles.png")

many thanks in advance!