This study uses the Beam Propagation Method to examine the performance of a basic single mode-multimode-single mode (SMS) optical fiber-based sensing head. By concentrating on important parameters like repeatability and hysteresis rate, the study seeks to evaluate and enhance the performance of the suggested sensor. The results show that the sensor is suitable for a range of applications due to its low hysteresis rate and strong repeatability. The results show the complete region sensing head was particularly more effective and sensitive to measuring changes in the close-valued refractive index (RI) which is highly essential for monitoring and categorizing biochemicals is one of the major objectives of this work. The findings show that the suggested SMS optical fiber sensor head can be used successfully for a variety of purposes, including biosensing and environmental monitoring. In the proposed design, we achieved a 19% improvement in sensitivity in the full-region sensing configuration compared to the interface-region sensing configuration.