Great write up on your link. I've done the same sort of testing, albeit a little less controlled and with out the great graphics.
I also found my original 13 year old XS and the CTX were very closely matched. And the perpendicular vs parallel is the whole key to understanding iron masking. Basically either detector can see a coin under a nail only if it is perfectly aligned with the center web of the coil, you will get a diggable hit at zero degrees or 180 degrees, anything else a null. Which explains why no site is worked out until it has been detected from every angle.
I did find the CTX can show a perpendicular coin under nail in target trace only, no audio signal. I tried to use this feature but trying to stare at the screen constantly was impossible, and that there were also WAY too many false positives that showed some coin signal but turned out to be only ferrous when dug. I'm assuming these are signals that give iron falsing on my XS.
I still think Minelab made a huge mistake stuffing all the targets on the FE 12 line. With my older detector I can tell at a quick glance at the screen to see whether a target is worth digging. With the Etrac and CTX all that happens is the target moves a few pixels left or right.
Thanks for writing up your findings,
Chris