Allan, I think you'd also do yourself a favour to try what Ray suggested some posts ago - go back to basics and see where the focal plane is without the RCC (and with it too if you must).
Pointing at the moon with a sheet of blank paper will tell you exactly where the focal plane is, then you can move backwards from there. You might even be able to do this during the day pointing it out the window/door. Failing that perhaps a bright star that you can visually find the focal plane with just your eye.
I've been close to pulling out a hammer many times with new rigs/reducers, and went through this all over again recently with a friend trying to tame his new 12" RC. First of all work out where the focal plane is, THEN worry about putting all the bits of the filter train in to work backwards for spacings to get the camera sensor at that point. It really is incredibly valuable to know (within a cm or so) where that focal point is while you're having these sorts of problems.
Good luck! Must be very frustrating for you, but those photons have to be focusing somewhere!
I'm envious of your TSAG setup and have many times thought of emulating your QHY9 rig - sticking with the Orion OAG for now though.