The coldest part of the coil is often on the fan side. This is because the warmest air enters the back of the coil and most refrigeration circuiting is set so that the air hits the coldest part of the coil last. This can give a closer approach and more efficient cooling. Terminate defrost when the ice goes away last during a defrost, after all, any other location will leave ice there and it can build up. Adding defrosts or lengthening defrosts may eventually be effective but at the expense of room temp and certainly uses more energy.
The termination sensor is in the space that's icing up (front) it's a klixon type that is mounted to the cabinet with the sensor sticking out into the space between fans and front of coil - where can I move it?
I think I would remove the termination switch and install new. I use the ranco with the bulb that you can slide into one of the open passes if the coil. Part # I think is f1127 if I remember correctly.
I agree with Cavalieri85. Placing the sensor in the fins where the ice persists will guarantee a clean coil. We have found that to be very effective. You will have to force a complete defrost to clean up that location to get the sensor placed, but once placed the ice should never return.