The First-order Reversal Curve (FORC) method is employed to analyze the influence of intermolecular interactions and particle size effect on Light-induced Thermal Hysteresis (LITH) behaviour of 1D spin crossover systems. We have used atom-phonon coupling model in order to simulate LITH-FORC diagrams with different interactions strengths and various amounts of molecules. The obtained FORC diagrams are rather different, which make this method a very powerful characterization tool. Finally, a comprehensive image of the particle size and interaction influence on the statistical parameters characterizing the LITH-FORC diagram is presented.