Force closed polygons (-L) in plot

I’m using PyGMT to make a cross-section plot and I’m trying to force closed polygons for the lower layer (dark brown). I’m wondering if there’s a way to fix the issue in the below plot. At the ends of the polygon I want vertical lines leading to the x-axis.

I’m using the below code, which is equivalent to the GMT command plot -L+yb.

Documentation states the options are either +yb|t or +xl|r which closes the polygon to either the x or y axes, and to the top/bottom or left/right.

for k, v in layers_dict.items():
            frame=["nSew", "a"],)