Are you using LOD 0, if you export the actual body mesh and then import straight in to MD it has all the LOD, the lower quality LODs are slightly different. You’ll need to import in to something like blender and the lower LODs and just keep LOD 0, export that to MD and everything should be the same. I’ve just run some quick tests and everything seems to be comparable. The only thing to note is the skin offset of the Avatar in MD, when you import a new avatar the offset defaults back to 3.0.
Other than that I’m not really sure what’s going on, just make sure your MH mesh and your Preview mesh are the same meshes and also on LOD 0.
Please share if you have any updates.