XPT2046 touch screen, max output in 8 and12 bit modes

Hi circuiteers

I have an LCD TFT touch screen working well, with the XPT2046 module in 8 or 12bit mode for X & Y. However in 8bit mode I never get a value >2^7 ie. 128. This is inconsistent with 12 bit where I do see values >2^11. Have I done something wrong or is this expected behaviour in 8 bit mode? I don't see it documented anywhere but I have checked my types in the C code.