The ad placement looks fine - there's nothing wrong with it in regards to placement ToS, but you might want to consider moving the ad units so that they appear between the first & second post of each thread. This is a proven method of increasing the (otherwise very low) CTR on forums. I didn't have time to look through all of your threads, but is it a soft adult forum? I saw a few threads that had women in underwear. You might want to be a little careful with adult content as Google can be very strict with that kind of stuff.