Virtual Texture Data GetNumMips reports one fewer mip than expected

FVirtualTextureBuiltData::GetNumMips() can return 1 fewer mip than it should due to a potential clamping issue at the end of FVirtualTextureBuilderDerivedInfo::InitializeFromBuildSettings() where it is clamped to VIRTUALTEXTURE_LOG2_MAX_PAGETABLE_SIZE (12) . The clamping is presumably to make sure that the texture can fit in the page table, so any clamping should be against VIRTUALTEXTURE_LOG2_MAX_PAGETABLE_SIZE + log2(TileSize)

Create a Virtual Texture of size 4K or above. Look in the texture editor at the number of mips reported. Note that it gets clamped at 12. Convert to a regular texture to see correct behavior.