No grey values are simple variations in numbers from 0 to 1, so 0.5 would be pure grey or 50% White and 50% black. There are a few things which can cause a bit of a discrepancy between the Material Editor and the Level. One of the big ones is how our Material Editor shows Metallic and Roughness values. Since those values are specular in nature and tend to be based on reflection actors placed in the level, the material editor attempts to simulate that effect with a generated cubemap based on the default level (cloud skybox). Since in your actual level you do not have a reflection actor nor any scenery to form a cubemap the level is using pure white specular colors.
Try this test, going back to your original setup (lose the multiple which BTW was set up correctly). Place your mesh in the Default map (Minimal_Default.umap) and see if it looks closer to what you are getting in the material editor.
The big take away I think for your work here is the reflection actor in the level will provide a cubemap which gets added into your metallic and roughness maps based on how close the value is to 0 / Black (Roughness) or to 1 / White (Metallic).
Thank You
Eric Ketchum