Mysterious scale factor for MERL BRDF?

[shocker-0x15]

Hello,

I have noticed that this code uses a scale factor x2 for MERL BRDF data: https://github.com/wjakob/layerlab/blob/3e5257e3076a7287d1da9bbd4ee3f05fe37d3ee3/src/layer.cpp#L530 Is there any basis for this value? or is this just competely ad-hoc? (I certainly feel materials look too dark with raw MERL BRDF, but I'm not sure the reason.)

Best regards,