I wonder how to set the size of the subplot when figure contains multiple subplots (5 × 2 in my case). No matter how big I allow the whole figure to be, the subplots always
Just switch figure size width and height from:
fig = plt.figure(figsize=(20, 8))
to:
fig = plt.figure(figsize=(8, 20))
to use the whole page for your plots.
This will change your plot from: