Essentially, you want to adjust the WPO or XYZ of the vertex by something to move it. But you also need a vector/direction along which you project that vector/magnitude. If you simply multiplied the Zcoordinate by .5 for the entire mesh, you would likely get something very odd, vs the flat-topping you seem to be asking for.
Otherwise for just raw-scaling of the mesh bigger vs larger, you can do something like this:
vs:
So, the short version is WPO is where it’s at, but depending on WHAT you want to do, you gotta figure out the maths for yourself. If you want to only scale parts of the mesh you will need to calculate the alpha for yourself.
In my example, I use the vertexnormal in worldspace so it’s always pointing ‘out’ from the face of the mesh, generally ‘out’ from the center, but complicated shapes being what they are, you might need to make something more elegant to calc an alpha-mask.
NOTE: adjusting the WPO this way does NOT carry over to collision, it’s visual only.