Alarm To Protect the Bed Contents

I just got a Viper 5701 installed in my 09 Taco 4 Door, Digital Tilt Sensor, remote start, front and rear Power Window Control and Field Disturbance Sensor.

It works great, but the Field Disturbance Sensor was to protect the back 2 feet of the bed (if I had something in the back of the bed you would get the warn away alarm). The guys at Kar Tunes are great, but we are stuck. The Field Disturbance Sensor is turned up so much that walking by the truck sets it off, yet nothing in the back.

Any ideas on how to protect the Bed the same as a convertible? If you reach into it, alarm/warning?

I do not have the install guide, but would turning the Field Disturbance Sensor 90 degrease put more radar out the front and rear windows, than the sides, and help 'see' the bed?

thanks in advance...