Actually the downmost position on a Dahon is fine for me (6'2" tall). Smaller riders usually need to hacksaw the telescoping part of the stem to get it lower (yes, that' a bit irritating, but it is to make it extend long enough to provide the under-the-axle fold for those who have a rack and a fully stuffed bar). I don't see any compromise for folding. Only geometry problem I see on Dahons is, that they do not provide enough reach for taller riders. People above 6ft might want an ahead stem to improve the reach, then it is fine.
feijai, which BF do you own? A Tikit? Could you explain why you prefer it over your Helios specifically? I would be interested.