We are starting to get into defensive skiing rather than call outs, but here goes:
I almost always pass someone when they reach the apex of their turn and are starting to turn the other way. That way, even if they deviate from their cadence (I assume people will, most people aren't that consistent), I can't possibly cause a collision because I have timed my pass with their change in direction. I also frequently check my six before expanding my turn radius and stop if I am caught up in traffic.
Relying on someone to call out an unexpected pass isn't the best strategy. Someone skiing poorly enough to cause a collision probably doesn't know that "on your right" is even a thing. Best not to rely on that from someone making a dangerous pass. Downhill skier always has the right of way, but I ski with the assumption that the uphill skier thinks they do.
I can't ever remember being hit or having a close call while moving.