A couple of thoughts based on my observations of top level skiers in the various disciplines. Bumps, steeps and short radius groomer turns, lots of separation. Medium, and especially large radius, not so much. That is not to say that there is none. Have some fun searching for photos of the same skier in the different disciplines, and of course looking at Ron le Master photos is great too (RIP).
You mention pivot slips (I assume with no issues staying with feet right over a real or imaginary line?) but these in and of themselves do not guarantee that the separation is happening. What has the feedback been from your instructors on the short radius not in bumps?
Maybe a video link or upload would be super helpful of you doing short radius on groomed and in bumps as well as medium long turns.
As instructors we all have slightly different takes on the separation matter, and I like to defer back to one of my trainers on the national PSIA team, as I asked her the question, and she confirmed my standard answer to how much of it: it depends (on radius and skis and skier and conditions).
In terms of how I would help someone who needs more of it, I would begin oddly enough with the head and the vision. In most cases, the head and eyes, especially in bumps, tend to revert back to looking across the hill rather than down the hill. I am convinced that if we are looking across and the skis are more or less across in order to scrub speed as well, there is about zero chance of being able to have the torso face down the hill. Start with where you are looking and your head is facing. If you have someone who can watch you in bumps have them tell you if they saw the entire goggle from below or if they ended up seeing both sides of you goggle straps as your head turns to look at where the next bump is.
Once the head/vision matter is consistently looking down hill, return to the pivot slips, and then start applying them to bumps, as that is what that drill really helps with in my experience.
Another thought has to do with ankle/knee/hip flex. If we don't have enough flex, it is to have the skis difficult pointing in a direction that is slightly different from the torso and head, as the range of motion is greatly restricted. It can be done, but then it is mostly twisting of the spine, rather than turning of the legs in the hip socket that is creating the separation. Not as powerful and stable.
I do have some drills I like but they are hard to describe. One I call 'poles to pits', another that is used a lot more often is having a person lay on their back with knees and hips each bent at 90 degrees and rotating the femurs to have the knees pointing first to one side then to the other. That is the ultimate separation drill as the back can remain stationary facing at the ceiling or sky, while the legs are doing all the work. Another one, also to convoluted to describe with words, involves no poles, and pushing the uphill knee with the downhill hand at the end of the turn.
For angulation, which is also part of good skiing, but slightly different from separation, as I can have one without the other and vice versa, I like outrigger pole drills, which have to be done carefully as they can create a horrible stance for some skiers.
USSA drill here is a link to USSA where kid and adult are seen doing the drill.
Both PSIA and USSA have drills for each major aspect of skiing that can be very useful.
Best of luck.