hey man!
I just learned FS Tail, took me 6 years to learn it hahahahah but what really helped me get it was try popping considerably taller than the ledge so I have time to rotate myself well enough and put my weight on it.
Before, I tried to ollie straight into the Tail, without much air time.
Maybe that helps you out!
I think that is why it does not roll, maybe my weight is not falling on the tail, as you can see sometimes I step on it but it stays at a stop.
Maybe, man! Try it out and let me know.
Another important thing is body position. Since you have to rotate 90 and stuck your foot on the tail, it's easy to just stall. And if you put your weight too much backwards, you will slip off. Try finding that balance and I'm sure you'll get'em
I will keep trying, many friends tell me that it is like a lipside fs but the truth is I think this is more difficult.