How to set width and heights for nodes with images propertly?

[uduse]

The script looks roughly like follows:

graph = pygraphviz.AGraph(directed=True, imagepath=image_dir, dpi=72)
graph.node_attr.update(
    imagescale=True,
    shape="box",
    imagepos="tc",
    fixed_size=True,
    labelloc="b",
    fontname="Courier New",
)
graph.edge_attr.update(fontname="Courier New")

graph.add_node(0, label="some label", width=2.5, height=4, image="image_path")
# Add all other nodes and connect them up.
for i, node in enumerate(nodes):
    graph.add_node(
        i + 1,
        label="some other label",
        width=2.5,
        height=4,
        image="image_path"
    )

However, when I generate the DOT file with the script, the width and height are overwritten to a different number for all nodes like this:

...
	146	[height=4,
		image="image_path",
		label="some_label",
		pos="2309,11952",
		width=3.5];
...

The magic numbers width=2.5, height=4 are picked by me through trials and error to generate a good looking graph. However, when I resize the image, the whole thing changes disproportionally.

Before I resize the image:

After I resize the image and changed the DPI:

What I want to achieve is to set a fixed size for the nodes (the labels are usually the same size), and let the image fill the top half of the node as much as possible keeping aspect ratio. Is there a better way of doing this? 🤔