Multiplex 4000 More Programming Questions
To alter centre whilst moving the travel end points along with the centre, use the servo centre, not the control centre trim. Put the control centre trim back to zero. Go to menu 1, servo, Centre+lim, adjust the centre value to probably +10%. Servos go to true centre and stay there while this parameter is activated so you can't adjust it "live", have to make an adjustment, come out of the centre parameter say by pressing top right triangle button and see where the servo goes to.
There is another hint in your explanation. You say travel is maxed at 109%, I take it you mean servo travel. If your LIMIT is still set at the default 100% then your servos are stopping at 100% and are not travelling that last bit of stick movement. Move the stick slowly and watch the servo carefully, you will see the servo stops moving before you get to the end of stick movement - the last ~1/10th of stick movement is wasted. Menu 1, servo, centre+lim, alter limit value to 109 in both directions.
BTW, be careful about asking to reverse the trim! You can actually do this, have the trims working the opposite direction to the controls which makes a whole puzzling mess of trying to trim the plane in flight!
Harry