In the simulation of dilute gas-solid flows such as those seen in many industrial applications, the Lagrangian Particle Tracking method is used to track packets of individual particles through a converged fluid field. In the tracking of these particles, the most dominant forces acting upon the particles are those of gravity and drag. In order to accurately predict particle motion, the determination of the aforementioned forces becomes of the upmost importance, and hence an improved drag force formula was developed to incorporate the effects of particle concentration. This study examines the individual effects of particles located both perpendicular and parallel to the flow direction, as well as the effect of a particle entrain within an infinite matrix of evenly distributed particles. Results show that neighbouring particles perpendicular to the flow (Model II) have an effect of increasing the drag force at close separation distances, but this becomes negligible between 5-10 particle diameters depending on particle Reynolds number (Rep). When entrained in an infinite line of particles co-aligned with the flow (Model I), the drag force is remarkably reduce at close separation distances and increases as the distance increases. The results of the infinite matrix of particles (Model III) show that, although not apparent in the individual model, the effect of side particles is experienced many particle diameters downstream.