Now that you've (most likely) ruled out tune as the culprit of your troubles.
My suggestion would be to measure the delta on this set-up, as you know you're comfortable on it. Use a caliper measurement tool (if you don't have one, you can pick up a cheap one at Home Depot or Amazon for like $5-10). Get "real-world" data for what you feel comfortable on. Then measure your others...compare and see how close they are.
Then experiment a bit, stand in your boots in your house...on a flat surface. Do you feel balanced? Can you squat down to have your thighs parallel to the floor (like if you were in a racer's "tuck" position)? Or do you feel like you're falling backwards? Can you get your femurs level? Play with different stances, what's the most comfortable and balanced?
- Tuck a magazine under your heels (this acts like a positive delta on your bindings, which also changes your forward lean)
- Magazine under your toes (this acts like a negative delta on your bindings, or a "gas pedal")
- Tuck a magazine behind your calf between shell and the liner (only tuck it in a couple inches, pushing your knees forward)...this adjusts your forward lean only, like a spoiler in your boots...no delta change.
Based on what you measured on your Sheeva's, does your experiment in your ski boots line up to what position your Warden demos are achieving?
Get to a point that you feel balanced off of your skis. Then try putting on your skis. See if things line up.
Here's a helpful resource for explaining a bit more about what I'm trying to explain here:
https://skierlab.com/are-your-ski-boots-helping-you-be-a-bad-ass-or-just-bad/