Using a Non-equilibrium Green’s function (NEGF) approach, a set of experiments is suggested which can provide indirect evidence of the fine and non-local electrostatic tuning of the onset of spin polarization in two closely spaced quantum point contacts (QPCs) with two sets of in-plane side gates (SGs) in the presence of lateral spin-orbit coupling (LSOC). The conductance of the two closely spaced QPCs or four-gate QPC is studied for different biasing conditions applied to two leftmost and rightmost SGs. When calculated as a function of the common sweep voltage Vsweep applied to two of the SGs, the conductance plots show several conductance anomalies, i.e., below G0 = 2e2/h, characterized by intrinsic bistability, i.e., hysteresis loops due to a difference in the conductance curves for up and down sweeps of the common gate voltage. The hysteresis loops are related to the co-existence of multistable spin textures in the narrow channel of the four-gate QPC and are very sensitive to the biasing conditions on the four SGs. The shape of the conductance anomalies and size of hysteresis loops are different when the biasing conditions on the leftmost and rightmost SGs are swapped. This rectifying behavior is an additional indirect evidence for the onset of spontaneous spin polarization in nanoscale devices made of QPCs. These results show that the onset and fine tuning of conductance anomalies in QPC structures are highly sensitive to the non-local action of closely spaced SGs. This effect must therefore be taken into account in the design of all electrical spin valves making use of middle gates to fine tune the spin precession between QPC based spin injector and detector contacts.