There is not perfect solution for interpolating voxel intensity to mesh vertices. One could argue for maximum intensity within a search radius, nearest neighbor, trilinear interpolation, etc. Surfice is a visualization tool, and the per-vertex colors make the most sense for statistical calculations estimated per-vertex not per-voxel. I see this issue as out of scope for a visualization tool. Feel free to write your own Python tool using nibabel to provide your own preferred solution for this problem.