define small...like a "light beer"? The lowest I have made is a 1045 beer, still working out what the FG will be...but I am purposefully adding extra sugars to bring down the FG due to a high mash so it isn't exactly correlative. the lowest I have seen for beers around here is a SG is 1038. What kind of beer are you looking to create? From what I understand, once outside most style guidelines, the % malt grain bills are not as useful as they are with-in the guidelines. For such a small grain bill a smaller amount goes a bit further than the same % does in a medium/large batch. Atleast, that is what I am seeing on a wheat I am making when trying to add a little red color with a bit of Crystal 120L.
for something really low, like a 3-4% beer, that gives you a starting gravity around 1.027-1.030, so what you can use is fairly limited. I am as much into specialty grains as the next guy, but when using such a low gravity I would recommend...restraint...on the specialty grains.