Here is the chiasm in Mark 15:16-20.
All of the pieces of the trial and crucifixion are now assembled. It's clear that Dart was right about almost everything except Markan centers, which are complex. Here the writer of Mark alternated the centers. Going by the centers only....
Sanhedrin Trial: ABAB
Pilate Trial: ABBA
Mocking Scene: ABAB
A clear pattern.
I'll have the crucifixion up in a few minutes after I tinker with it a little.