Muonium transition rates are modelled for n-type Si based on parameters obtained from previous RF-μSR studies. We identify several different Mu charge cycles and the temperature region over which each dominates as the main source of longitudinal-field μSR relaxation. A new three-state -/0 cycle is established as most important at the highest temperatures and a modification of the rate expression for activated capture is proposed to reconcile apparent discrepancies between relaxation data and the existing model of Mu dynamics.