resolve as By Design
That is a surprising plot. Does it stay that way when you change selection? It really looks like you have enough space to plot the labels horizontally with a larger font.
The font size will increase if you give the plot more vertical space, i.e. make it taller. You are also not required to keep the names as they are. You can modify them either by using Edit > Manage Results, and double-clicking the names to edit them. Or if you put Replicate Name in a report in the Document Grid, that also is an editable field, if you don't need your plot labels to match your file naming.
The x-axis font scaling code is pretty challenging but required to avoid the x-axis text from taking so much space that it forces the plotting area to zero, in which case, our graphing package completely blanks the pane containing the plot, which proved to generate a lot of support requests. Obviously, this is a support request generated by the font scaling approach, but there have been far fewer of those than there were with keeping the normal font size for the x-axis labels and allowing them to consume the plot area. It seems most people can figure out a way to get a usable font size by increasing the plot height or changing the replicate names.
So, we are going to stay with this implementation for now. Thanks for your feedback. We will certainly consider whether we are being too aggressive in the scaling or in your case, missing an opportunity to change the labels to horizontal text with a larger font.