Thanks for the nice comparison, the XHP70.2 mod (with TA driver) is in the planning for my GT also so I’m glad to see it performing so well.
About the lux-readings: I recently (link) compared the LX1330B luxmeter (which is the one I think I see you using) to my high end Mobilux meter (which should be as accurate as you can possibly buy in a portable meter) and my LX1330B meter at least reads the cool white 70CRI XM-L2 in my Sunwayman D40A 9% too high, and a (70CRI) 4500K led 7.5% too low. That is 16.5% apart, so the spectral error of the LX1330B alone could already account for the reading difference that you find between the cool and neutral XHP35 Hi emitters in your GT’s.