NMI: Please open a support ticket on icomp.de (eMail page) and file a bug report, so I have more detailed information and I've got you in the support database.
keropi: You can create your very own VGA modes in order to make games full-screen. Open the config tool, press and hold the right mouse button and choose "VGA modes" from the Config menu at the top of the screen. Keep in mind that Indivision AGA MK2 will never scale data. Scaling will only be done by your monitor. If the picture is scaled in order to reach full-screen, you will always get a blurry picture, depending on the scaling capabilities of your monitor.
I can't promise if there will be an option for line-tripling or even more. There's known bugs that I need to fix, and I don't want to open new construction sites when old ones aren't closed.