Their problem is directly related to the mid wing concept.
The "downwash" gives lift, that enters the chassis at the root of it's support, despite what many say, it can't route to anywhere else.
Yes all the others have "downwash" too, but with most expressing the negative pressure almost directly over the most powerful element of under floor negative pressure point. The transaction between those two is directly linked longitudinally in the chassis, one above the other in effect.
Mid wing displaces that effect far further forward, then lifting the front of chassis as speed rises. Increase in diffuser/floor negative pressure nearer to rear just makes that front lift more prominent. Listen to comments on second day of Bahrain testing. Something like "complete, mysterious loss of front downforce" when they (by wispered account) dropped the rear ride height.
There's no adjustment on mid wing, they're stuck with that fixed lift profile, only putting on more and more front and rear wing appears to counter this. Then the drag is there. It's like a see-saw, push down on one end and the other comes up, giving rise to drivers observation of never being able to balance the car.
There's no real separation of control downstream on zero pod either, it's all got to be positioned by that one mid wing to condition so many defining aspect of post-mid to rear flow streams. There's just not the tools there to operate effectively, especially if aero time is limited. They also demonstrate that they don't understand it, arriving at each track being a surprise in performance terms, and whether that's going to be a plus or a minus surprise
