Optical fiber sensors based on the total light transmittance are widely used to measure the volume fraction of particles in suspensions. However, the sensor response depends not only on the volume fraction but also on the particle size. The particle size effect is studied for a sensor configuration consisting of two linear arrays of fibers on each of two blocks: the emitting and receiving blocks. These two linear arrays are arranged with three adjacent fibers (one fiber on the first array, two fibers on the second array) forming a perfect triangle. The almost superimposition of the calculated sensor response versus the extinction factor for different particle sizes allows for the application of single- curve models. Two single-curve models that describe the sensor response for all particle sizes ranging from 36 to 200\mu \text{m} are proposed. The models are validated by Monte Carlo simulation for different particle sizes and are valid within a detectable volume fraction. The single-curve models proposed provide an easier approach to creating a database for sensor calibration for suspended sediment concentration measurements.