I am using WLP002 - English Ale Yeast - in my current batch, a Young's double chocolate clone. According to the manufacturer's product page, this yeast is highly flocculant.
The beer remained in the primary for 15 days. After this time, the gravity had fallen from an OG of 1.070 to 1.021. This is a 70% apparent attenuation, which is the top end of the expected range for this yeast. There was a lot of yeast still floating on top of the beer, but I racked to the secondary anyway. Here is a picture of the secondary after three days. That is yeast on top. Last night, after two weeks in the secondary I used a small spoon to pull a bunch of this out and verified by smell that it is definitely yeast. I also took another gravity reading and found that it fell from 1.021 to 1.018 in the secondary. I now have an apparent attenuation of 74.2%, kind of high for this yeast. Yet, the yeast remains atop the beer.
Why is the yeast not flocculating? Might it be that the high amuont of lactose (12 oz.) and/or cocoa powder (6 oz.) in the beer is making the beer more dense than the yeast? I'd like to see this yeast fall to the bottom before I bottle, else it will end up slurrying the beer.