I do not understand why in the following example, if I set patch_alpha=1.0, I do not see the shadow effect.  I would expect to see it for the the rightmost four bars, where the original bars do not entirely occlude the shadow, so even if alpha is 1.0, there are parts of the shadow that are not behind the original bars and should still be visible.

import matplotlib.pyplot as plt
import matplotlib.patheffects as PathEffects
import numpy as np

fig = plt.figure()

# sime bar shadows
x = np.random.randn(1000)

n, bins, patches = plt.hist(x, bins=7)
shadow = PathEffects.withSimplePatchShadow(offset_xy=(10,-10), patch_alpha=0.8, shadow_rgbFace=(0.25,0.25,0.25))
for p in patches: