Here are my Blender FBX export and UE4 import settings, if this might help at all. I would recommend creating a new blank project with two different skeletal mesh cubes, each share the same skeleton structure, but the first one is twice as large. Make sure both have their scale applied in Blender before exporting. Import both of the FBX files into UE4.
Make a copy of this project and pack it as a .zip file using 7zip. If bigger than 5.2 MB, upload the .zip file to a safe file sharing site (like Google Drive) and paste the link here. Now Epic staff will be able to test to see if when retargeting the large one to the small one, the small one comes out bigger than it should.
