Update: I figured out how to work around this issue by utilizing the external image widget.
The new release with auto width and height helped quite a bit. Along with my discovery that if I change the from=value in the image URL to a negative number, and remove the to=value I can dynamically specify how far back to graph. Then the Target URL: allows me to set up correct navigation.
It’s a bit of a hack, but I thought it might help someone else out there. Below is a non-functional example of my External Images widget settings:
Target URL:
https://nms.example.com/graphs/type=munin_graph/device=83/plugin=custom-resources