I see it's a frag, so probably just doesn't have a secure, broad enough base yet.
Give it some time to grow out.
When shrunken it is more rigid, thus appears to stand better.
If polyps are out and otherwise healthy, I'd say just give it some time to do it's thing.
On a sidenote, pulsing sinularia?!?! Very cool! I've only read about this, and never seen one in person.