visualizing BSDFs with BSDFviewer and rmtxop -fc

edit

I know the question about BSDF direction has been asked and answered all over the radiance web, but I'm still confused and have a new question about the various ways of viewing BSDF data and how they make sense of the forward/backward issue:

When I make an image of a BSDF.xml file that has data for both forward and backward directions, which matrix does it return? Matching pixels to patches on the BSDFviewer, it matches "Visible Transmission Front" in distribution but the values are not exactly the same. What confuses me about that is when using rmtxop in the 3-phase method, I assume it is using the back transmission/reflection data. Any explanations?

Thanks