Manga has never looked brilliant on the Forma when I have tried reading it because the screen size doesn't match the page format. As there's no reader with a screen size between 8" and 10" available (at least in the UK) I'm not exactly spoilt for choice.
I just had a quick look with a ruler and the forma screen diagonal is 20cm (a touch under 8"). My 10" tablet screen has a diagonal measurement of around 25.5cm (a touch under 10"). My paper copy of Death Note is 23cm (just over 9") across the diagonal. So a 9" screen size is probably the minimum for Manga to display the correct size. Very rough measurements, sorry
