Recently proposed improvements of the μSR (muon spin rotation) technique include among others the use of position-sensitive detectors for the revelation of decay positrons. Unlike their high-energy particle counterparts, these detectors present specific peculiarities arising from the need of a relatively fast timing and from significant multiple scattering effects. By using advanced numerical simulation toolkits, such as Gᴇᴀɴᴛ4, we explore the expected detector performance and possible ways for its optimisation. Intrinsic limits, finite pixel size effects, as well as the many parameters influencing the detector behaviour (distance, extension, angles, etc.) were thoroughly analysed and quantified, thus providing a valuable guide in prototype building and testing.