So about the auto-size font - the logic is correct, but there was an artifical limit of 59 for the calculated font size (without the fixed page size feature, I never anticipated anyone needing a font size greater than that due to how the fonts would scale with the screen density). I have now increased this to 100 to match the maximum value that is selectable on the text display settings. I will likely increase this after I redesign the settings dialog.
One thing I want to help explain - without the page size being explicitly set, the font sizes are dynamically scaled based on the density of the screen. Most Android devices use scaling factors between 2 and 3, meaning any lyric/chord text size you pick on the text display settings dialog is actually being multipled by a value between 2 and 3. Once a fixed page size is selected, I cannot scale the font like that, as it would cause completely different results on devices with different screen densities. So I scale the font size based on the difference between the resolution of the screen and the page size resolution. This effectively resizes the resulting image so that it fits the screen. So if you had a page size of 1200x1600 (width by height), and the page size is set to 600x800, then the font will be scaled by a factor of two to ensure that the image is "stretched" to fit the screen, however this provides a much sharper result than me rendering a 600x800 image and just stretching it to 1200x1600, as then the font would be blurry. The reason I'm explaining this is because you mentioned having to significantly increase the font size in the text display settings to get the desired output. That means you basically figured out the display scaling factor of your screen, which is higher due to the high resolution of the screen or the settings you have selected (as the BOOX devices let you choose the DPI for the application in the optimization settings).
I know that may all be a little confusing, but it's implemented correctly to ensure that the resulting image looks the same across devices of different screen resolutions. If you select 800x1200 as the page size, for example, and you render that file on a 1860 x 2354 screen, it's going to nearly double the size of the image in order to make it fit the screen (which is actually nearly doubling the font size that is used), but the resulting image should appear effectively the same. Conversely, if you specify 1860x2354 as the page size and you put that on a 800x1200 device, it's going to have to shrink things down by a factor close to 2, so it will be harder to read as the font will look smaller. So I might advise using a smaller page size if it's important for things to be more legible on the smaller device, but that just means the font will be larger on the higher resolution device, which may not utilize the available page size effectively. There is no way around having to make this compromise if you have devices with significantly different resolutions.
Mike
One thing I want to help explain - without the page size being explicitly set, the font sizes are dynamically scaled based on the density of the screen. Most Android devices use scaling factors between 2 and 3, meaning any lyric/chord text size you pick on the text display settings dialog is actually being multipled by a value between 2 and 3. Once a fixed page size is selected, I cannot scale the font like that, as it would cause completely different results on devices with different screen densities. So I scale the font size based on the difference between the resolution of the screen and the page size resolution. This effectively resizes the resulting image so that it fits the screen. So if you had a page size of 1200x1600 (width by height), and the page size is set to 600x800, then the font will be scaled by a factor of two to ensure that the image is "stretched" to fit the screen, however this provides a much sharper result than me rendering a 600x800 image and just stretching it to 1200x1600, as then the font would be blurry. The reason I'm explaining this is because you mentioned having to significantly increase the font size in the text display settings to get the desired output. That means you basically figured out the display scaling factor of your screen, which is higher due to the high resolution of the screen or the settings you have selected (as the BOOX devices let you choose the DPI for the application in the optimization settings).
I know that may all be a little confusing, but it's implemented correctly to ensure that the resulting image looks the same across devices of different screen resolutions. If you select 800x1200 as the page size, for example, and you render that file on a 1860 x 2354 screen, it's going to nearly double the size of the image in order to make it fit the screen (which is actually nearly doubling the font size that is used), but the resulting image should appear effectively the same. Conversely, if you specify 1860x2354 as the page size and you put that on a 800x1200 device, it's going to have to shrink things down by a factor close to 2, so it will be harder to read as the font will look smaller. So I might advise using a smaller page size if it's important for things to be more legible on the smaller device, but that just means the font will be larger on the higher resolution device, which may not utilize the available page size effectively. There is no way around having to make this compromise if you have devices with significantly different resolutions.
Mike