I am not sure what your structure is. Check for relation to threshold voltage of the electrical gate, if the other gate is sensing. Some idea for coupling "front" and "back" of organic semiconducting films can be found in
O. Marinov, M. J. Deen, J. Tejada, B. Iniguez, "Impact of the Fringing Capacitance at the Back of Thin-Film Transistors", Organic Electronics, 12(6), 936-949, 2011; ISSN 1566-1199, DOI: 10.1016/j.orgel.2011.02.020