The throttle cut will always default to P1 on the throttle servo curve, so you need to set the encoder direction, in the controls menu, so your minimum throttle is at P1 and max at P9. I am not sure why the slider when fully up is only going to P3, this would suggest the encoder is still reversed and this is the trim position, as the trim offsets the control position and on throttle this works when the throttle is at the minimum position.
You need to go into the assign controls menu, enter the line where the throttle encoder is and push rev/clr or move the control to the minimum position and then push enter again, this will set the encorder direction, the asterisk * will show when the control is at the minimum position. You can then set your servo curve accordingly.
On my MPX Heron I use the opposite slider to you (slider G) and my throttle servo curve moves from -100% at P1 to + 100% at P9 in a straight line, throttle cut moves the control to the P1 position, with throttle cut off the control moves to wherever the throttle trim is set with slider G in the minimum position and then raising slider G moves the control input to P9.
