I corrected post nr 501 with all them mixer settings regarding aileron differential.
During vertical rolling (a manoeuvre best to check if it rolls axially) I still saw the nose describing a circle. So eventually I completely discarded the differential setting. It rolls much nicer now, but I might do more testing to fine tune. In one delta jet a while ago (Graupner Hotspot) I even needed "negative differential" to get it rolling axially...
The Xcal has become my favorite jet to fly, easy to take with me (tail booms and stab fitted to the fuse) and very forgiving to fly, spins, even flickrolls (but close to the stall speed region for not overstressing it) are in its envelope. Touch and goes are my favorite!