My wife worked at NASA Ames Research Center where they figured it out using the 80 foot x 120 foot wind tunnel to test many variations of parachute configuration until they found one that worked reliably.

You can’t model parachutes opening as that is in the domain of turbulent flow that computers suck at. It’s simply too computationally intensive, even with TODAY’S best supercomputers.

But with good old wind tunnels and physical test articles you can figure it out. But it takes time and having a Full Scale facility like they do at Ames.

And they have a fixed design with a now unchangeable (I suspect due to schedule) volume to fit the parachute into, so it will be interesting to see if they get it fixed or miss the launch window.

I hope they can solve it, because ExoMars has the capability to do some amazing science if it can make it to Mars intact.