asymmetrical stack with edge coupled differential stripline formula?

Hello all,
I've been searching and have not been able to find a formula for calculating the impedance of differential lines on inner layers where the dielectric above and below it is not symmetrical. I've seen plenty of examples of symmetrical stackups, but that would not help in my case.
Does anyone know what the formula would be for this?
Thanks!

You might look at Transmission Line design Hdbk Brian Wadell or Coplanar Waveguide Circuits, Components and Systems by Rainee Simons if you don't find what you need in Wadell.

Polar's Si9000 software might also be helpful.

I did not look for your particular configuration. You can have that fun.