Reproduce

1.Create new GameObject and attach VRCAvatarDescriptor

2.Create new Cube as child of that GameObject

3.See inspector of that cube. Open materials in MeshRenderer of Cube

4.BuilderPanel shows 12 triangles.(Cube has 12 triangles,right)

5.Edit materials any large number.(in screenshot, 1024)

6.BuilderPanel shows 12 triangles.

Expected

BuilderPanel shows 12x1024 = 12288 triangles

>If a Mesh contains more Materials than sub-Meshes, Unity renders the last sub-Mesh with each of the remaining Materials

In this case, Cube mesh(sub-mesh) will be rendered 1024 times. so I think AvatarPerformanceRank should count this.

SDK Avatar 3.9.0