So... dynamic carving on bx or free ride board assuming either soft or hard the binding angles for optimal mechanics are....
Good assumptions on both counts.
A. Riding a negative angle on the back foot is a good way to prevent a full, rebound driven, elastic sweep of the board through a heel side turn. Consider that in order to do so, the pressure wave under the board needs to move from the tip right through to (and out of) the tail. With a negative rear foot angle, the wave stalls under the rear heel, somewhere near the mid length of the board. Any energy remaining in the system needs to go somewhere, so if the rider hangs on to the edge too long, the snow under the edge will probably blow out as the load spikes, leading to 'chatter'.
B. If the highbacks are not set 'correctly' the board will most likely twist while on edge, and/or, the rider will not be in a good position to 'work' the board, on account of lost ROM or excess muscle tension.
(In the event you don't already realize this, a board 'twisted in the cut' is trying to make a turn of two different radii simultaneously.)
All other adjustments being effective, you might try setting them up as follows:
Standing evenly weighted on both feet, with your hips in line with (perpendicular to) your front foot, rock lightly back to feel contact under your heels. At the moment of firm but not excessive heel contact, you should feel the support from both front and rear highback at the same time.
This is a baseline for sensible stance angles and widths.
May not be valid in all sales territories.
Season to taste.
So... Dynamic carving on unidirectional bx or freeride board. Assuming soft or hard, address binding angles for optimal mechanics.