I'm confused though.
1) the definition of pivot slip was "linked side slip...".
I always thought side slip has edge components. That's how we slow down in tight space, is it not?
2) I can keep the ski flat by standing tall and facing the tip. But it's really awkward to NOT tip the ski on edge when facing sideways.
Granted, that might be part of my problem of why I can't seem to be able to do a flat 360!
I think you've identified the source of your challenge. I don't think of the side slip as a slowing down or stopping mechanism. For me, it's a "get out of this hairy terrain" tool, aka, movement. When you are actively side slipping, your edges are released. When the edges are set, you're no longer side slipping.
ETA: But, to bring this back to the OP's issue, to be completely frank and not as discouragement, please get a lesson if you're interested in figuring out what you are/are not doing, especially if you're the type of learner that likes having a name for everything that you're doing. Given your ability level that you described in another thread, I don't think you're doing pivot slips; it's likely more of a smear.