Hi Peter,
Thank you for the feedback. You can use the height and width parameter to change the size of the graphs of a single time series. For example:
https://thingspeak.com/channels/9/charts/1?height=800&width=800
It sounds like you are looking for the ability to do this on some of the plugin data, like the "Chart with multiple series" one. We'll look into this feature request. For now, if you used a MATLAB visualization App to make your plots, you could resize it. See example below.
https://thingspeak.com/apps/matlab_visualizations/130578?height=800&width=800
I essentially have a MATLAB visualization that is pulling data from a channel using thingSpeakRead and plotting it using the thingSpeakPlot function. Does this workaround work for now?