How to take a layer above a sphere inside of a 3D matrix?

Let's say I have three n*n*n matrices Hx, Hy and Hz, each of them contain the vector components at that point in the real space. Inside of those matrices, there is a sphere, where it's a void (values are 0). By using isosurface I can get the sphere easily. How can I get a layer just above it and plot on the sphere? Code, pictures and matrices are attached. It should look like a sphere with vectors on top of it

fv=isosurface(sqrt(Hx.^2+Hy.^2+Hz.^2), 0);
DT = delaunayTriangulation(fv.vertices(:,1),fv.vertices(:,2),fv.vertices(:,3));
[K,v] = convexHull(DT);
trisurf(K,DT.Points(:,1),DT.Points(:,2),DT.Points(:,3))