Relating trigonal crystal field parameters ($D_\sigma$ and $D_\tau$) to real space distortion

Dear all,

I have simulated L-edge XAS data using trigonal distortion and was able to reproduce my spectra for a certain set of $D_q$, $D_\sigma$, and $D_\tau$. Now I am trying to understand what that implies in real space: Is the octahedron compressed or elongated and how much has the bond angles moved. I have checked Ballhausen but the trigonal distortion section is not very detailed. I was able to find only this paper regarding the issue: J. C. Hempel, JCP 64, 11, p4307(1976) however the definitions of the angles are not very clear to me. Any suggestions on how to proceed with this?

Many thanks! Heba