It's better to direct Vray questions to Chaosgroup since Autodesk doesn't make Vray, but the reason you are getting a black area on top is because your environment color is black. Use an HDRI or something in your environment slot or in the reflection override slot in your Vray ...
the scene is going to be receiving the lighting from our HDRI image twice. This is not an ideal situation as it increases render times and makes our settings less precise. Under Render Setup go to the [V-Ray] tab click the [Environment] roll out. Check [...
(*) VRayHDRI maps now declare their files to the Asset Tracker in 3ds Max 9; (*) VRayMtl has a new “hybrid” SSS model; (*) VRayMtl now has an “Envrionment priority” option to control environment override behaviour between different materials; (*) VRayMtl now has a “Roughness” ...
Materials and lighting go hand in hand. A realistic texture can easily be ruined by poor lighting. As such, you will be using an HDRI image that will serve as an image-based lighting to simulate a real-world scenario. You can download HDRI maps fromthis resource site. Modeling, Lighting ...