do you mix the fermcap in? if you put it into cool wort i think it has a tendency to sink out. i honestly don't know if this can be a problem, or it it will get mixed in as the yeast take off, but it's something i've been concerned about as i watch it sink to the bottom, so i'm suggesting it as a possibility. now i add it early on as i'm filling the fermenter, and then swirl really well to dissipate the drops, and it works well for me. that said, you didn't give any details about how much head space you are allowing, nor what yeast you're using