the rotation is around the rotation axis (which is actially the z- coordinate).
Axis1, axis4 and axis6 turning mathematical negative (e.g. a1 = 20° gives negative Y-value)
(A reason could simply be mounting gearbox upside down to have motor on top)
Axis2, axis3 and axis5 turning mathematical positive
You can find this in $Machine.dat checking for AXIS_DIR (it was also mentioned in one of my posts on the other of your thread)