I have Worm Fatory and stackable RM. You are right about the dangling. In time when there are less and less food in the lower tray/bin, they do migrate because I found there were less worms there. It is possible that they have gone to worm heaven but I didn't smell it, and saw more worms in the upper tray/bin.
How long? Months!

They dangle when you remove the tray because they were half way in when the tray was removed. Place the removed tray somewhere and wait a few minutes, they will all pull back into the tray.

But there are only so many worms in each bin. And if each is given 3 hours to crawl into the next bin then math mathmatically only two should be caught dangling at any time. Yet we find hundreds. I think they claim dangle locations. They like to dangle for some reason. I think they eat with their top halves while soaking up oxygen with their bottom halves. Ok I made up the math. But I guess that is how it is. Statistically how many worms at any given moment would be dangling if worms move up to a new bin once a month?

Before the tray is removed, the worms are half in each tray. They are only dangling because you pulled their home apart.

If you lift the bottom tray out of the catchment tray, you don't see many danglers at all - if any.

If you could perfect a method for getting worms to all do a single migration to a new tray, you would have solved the propblem of worms still being in the castings.

They go up, then down, then up, then down, then they shake it all about and begin again.

At least that is my experience.

I did my first purposeful harvesting of my flow-through today. The newspaper has rotted out along most of the bottom bars, and I wanted the VC for my strawberries, so I hurried along the bottom layer by prodding the stuff out with a stick.

I was on the floor, looking up at the bottom of the flow through at the bars, watching what I was doing, poking up at the lodged compost, when all these worms came poking out. Maybe a dozen or so, hung down, apparently checking out what I was doing down there, then when I got to the area they where at they disappeared. When I was done getting what I wanted, sifting at all that, and was cleaning up the porch and putting stuff away, I got down one more time and looked, and sure enough, maybe a dozen worms where there hanging out, just looking around. Or maybe I was looking at worm butts. Maybe they were mooning me.

Yeah, I guess worms need some entertainment too, LOL.

My flowthrough is suspended over the catch bin. The worms would dangle. When their toes hit bottom I think some decided to investigate. I changed the dangle room from 4 inches to 6 inches and had a lot less in the catch bin in the morning. I think because their toes could not touch base. There is no connecting side wall for them to climb down. Will check again tomorrow because they do this in the dark.