Thread making is an art. Threads (and which direction and how many pages they are going to go) often depends most heavily on the OP and the following three or so posts.
The magic is lost with the OP THEN THE BIG ASS AD, followed the responses. Thats what I mean by distracting. Im no longer thinking about OPs joke or my response. Im thinking about Amazon Prime ads.
If the ad was prior to the OP, then the ad is seen but it does not interfere with the flow of the thread. That's win/win. Sidebar ad is another good option.
@cook already explained that supporters don't have this issue so.....jokes on me there but that's my feedback. I think the ads would work just as well placed elsewhere. But this is not my site....but in think shytty ad placement will hurt a forum over the long run, newest not yet supporting users will experience those big ass ads.....