I'm ( jedi guardian aswell) are also losing aggro on stormcaller. But thats mainly becuase our dps are putting out to much damage at the start of the pull.
What bothers me most is that when tanking stormcaller i get no stacks of fully talented "Courage" and not a single Riposte proc when fighting hem. Its been this way at every try we made on this boss
I'm not a tank, but as a Sentinel I do have Riposte. Take a look at the damage type that Stormcaller does and the types that have to be defended for Riposte to proc. Courage may be affected just the same.