REW 5.30.9 Distortion screenshot aspect ratio

Hello,
I was sure that in previous REW releases I could select the aspect ratio for capturing screenshots on the Distortion tab, but currently I am looking at a greyed out selection with "as plotted" as the only option. What am I missing?

Thanks! I'm mostly looking to create screenshots using the same settings, and get a consistent image of the same dimensions that isn't dependent on the REW window size at the time of pushing the capture button. Defining the aspect ratio is probably the best method, alternatively, allow manual selection for vertical size.