qml - qmlscene root item sizing discrepancy

import QtQuick
import QtQuick3D

Item {
    // width: 800
    // height: 800
    View3D {
        id: v3d
        anchors.fill: parent

        environment: SceneEnvironment {
            clearColor: "green"
            backgroundMode: SceneEnvironment.Color
        }

        PerspectiveCamera {
            z: 600
        }

        Model {
            source: "#Cube"
            materials: PrincipledMaterial {
                lighting: PrincipledMaterial.NoLighting
            }
            eulerRotation.y: 20
        }
    }
}