Reporting Effect Size with VBM

I was recently asked about the effect size for my group contrast vbm data. Is there a “proper” to report this? I’ve seen a couple ways:

Peak voxel of cluster, cohen’s d - (doi: 10.1016/j.neuroimage.2016.03.045)
Cluster range and mean, Pearson’s r - (doi: 10.1016/j.mri.2015.07.014) - this was for a continous variable design and wouldn’t directly apply to my own data

Any information would be helpful.