Hi there, they sound like they need to be divided. Mine did the same, I have to divide them as soon as the ground thaws out some more. They may also need to be more in a full sun area, sometimes they flop if they aren't getting enough sun.
Good luck.

Last year I pinched my sedum by half in June and it made a huge difference. They didn't flop at all!

I have used peony rings, and have found some rings with a grid in them. I am putting a link to them below, but I have also, on occassion, found them at WalMart in the US.

Cheers.

Here is a link that might be useful: Grow-Through Support Rings

I am about to give up on autumn joy. I have pinched, cut down, and yet it flops. I'm getting rid of a lot this year.

I have sedum neon also which does not flop one bit.

Anytime I have a plant with a hole in the middle I pretty much assume that it needs to be divided.
Pinching is good too.
Might also be that the soil is too rich or getting too much fertilizer.

But as Primgal said, if they don't get enough sun they are going to flop. They want full sun (and not to be shaded by their neighbors either).

I love this plant all year 'round, and have several big drifts of a dozen plants or more in several places around my garden. Bonus that the bees love it as much as I do.

Good luck!
Patti