PIONEER aims to measure the pion decay branching ratio to a precision of 0.01%. To do this, pions are stopped in a highly segmented, fast-timing silicon target (ATAR) from which particle tracks and decay patterns can be extracted. In this talk, I discuss the simulation work being done to reconstruct the tracks of the pion and its decay product to enhance our ability to separate pion decay into muons from decays into positrons. Additionally, I discuss how the recent tests in the CENPA Tandem accelerator will inform this simulation and the design of the project as a whole.