Add external margins with constrained layout?

When generating a figure to save to a pdf file, I'd like to adjust the positioning of the figure relative to the edges of the page, for example to add an inch margin along all sides. As far as I can tell, the solutions to do this (for example, in this question) either:

1. don't work with constrained_layout mode -- applying plt.subplots_adjust() after creating the figure but prior to fig.savefig() messes up the constrained layout
2. don't actually quantitatively adjust the positioning of the figure -- adding bbox_inches="tight" or pad=-1 don't seem to do anything meaningful

Is there a straightforward way to adjust external margins of a constrained layout figure?

For example:

fig = plt.figure(constrained_layout=True, figsize=(11, 8.5))

page_grid = gridspec.GridSpec(nrows=2, ncols=1, figure=fig)

# this doesn't appear to do anything with constrained_layout=True
page_grid.update(left=0.2, right=0.8, bottom=0.2, top=0.8)

top_row_grid = gridspec.GridSpecFromSubplotSpec(1, 3, subplot_spec=page_grid[0])
for i in range(3):
    ax = fig.add_subplot(top_row_grid[:, i], aspect="equal")

n_bottom_row_plots = 10
qc_grid = gridspec.GridSpecFromSubplotSpec(1, n_bottom_row_plots, subplot_spec=page_grid[1])
for i, metric in enumerate(range(n_bottom_row_plots)):
    ax = fig.add_subplot(qc_grid[:, i])
    plt.plot(np.arange(5), np.arange(5))

fig.suptitle("my big label", fontweight="bold", fontsize="x-large", y=0.9)

# this ruins the constrained layout
# plt.subplots_adjust(left=0.2,right=0.8, bottom=0.2, top=0.8)

fig.savefig("temp.png", facecolor="coral")

Yields the following (I'd like to see more coral around the edges!):

from Add external margins with constrained layout?