Suuri could be translated as 'big' as well as 'large', no?
True. If DL doesn't accept that, then you can report it so the mods can add it as an alternative translation. "Suuri" is more common in the written language and "iso" in the spoken language.
Why not "big"?
Why not On the ground is a large red leaf. That is perfectly acceptable in English and reads that way in Finnish
Hoe to tell difference between "on the ground" and "in the ground"?