When Do Yeast Rafts Sink?

I brewed a batch of Double Dead Guy ale about five weeks ago. The first week was held @ 60 degrees during fermentation and the remaining weeks at 70 degrees for conditioning.

The yeast was Pacman.

Yeast rafts remainded after the krausen dropped and are stil there today. I moved the carboy around a bit an in attempt to get them out of suspension but they are buoyant and drifted back to the top.

I am ready to keg and not sure what to do, this is the first batch where the yeast didn't drop completely.

What suggestions do you have for me?

Also, can someone explain why yeast rafts are formed? This is my fourth batch with Pacman and the first with rafts.

Some of my beers they never drop. I just rack anyways, since the rafts are on the surface they dont really end up in the beer anyways.

Cold crashing could help.

It's at 70 degrees right now. How far down should I take it?