Physical Material Mask does not appear in the Material Instance Editor

Although MaterialInstanceConstant has a physical material mask and physical material mask map property, these properties does not appear in the Material Instance Editor's details panel.

1. Create a new Material Instance asset.
2. Open the material instance in the Editor.

Expect result

There is a physical material mask property and associated physical material mask section with physical materials map. (see Material Editor details for comparison)

Actual result

There is no physical material mask property or associated section of physical materials.