Normally the default position is for the initial posterior value for a parameter to be taken from the prior, unless the model defines a different method for choosing this.
However in the case of an image prior, the voxelwise value is not used for the initial posterior - instead the existing default prior is used, as if there was no image prior.
It would seem better for the voxelwise value to be used both for the prior and the initial posterior.
Normally the default position is for the initial posterior value for a parameter to be taken from the prior, unless the model defines a different method for choosing this.
However in the case of an image prior, the voxelwise value is not used for the initial posterior - instead the existing default prior is used, as if there was no image prior.
It would seem better for the voxelwise value to be used both for the prior and the initial posterior.