\subsubsection{Additional timing and energy results for 20 mm}
In figure \ref{fig:centroidposition-20} the delay peak position with DOI is seen to possess the same plateau as observed in the 30mm measurements. In this case the plateau is reached close to 10 mm for the wrapped measurements. Again the peak to peak range in the delay peak centroid is comparable to the scintillator crystal length. We can conclude therefore that the shift is predominantly dependent upon the geometry of the scintillator crystal. 