This paper proposes an interactive mechanism between both tiers of mixed-member electoral systems to explain high-level linkage in West Germany, that is, the dominance of district races by the candidates of the two largest parties at the national level. The distinctive feature of the model lies in interactive effects in terms of expectation formation. That is, voters under mixed systems are assumed to utilize national-level PR results to form expectations which, in turn, are used to vote strategically in the plurality tier. To sort out the independent effect of these kinds of interactions, this paper develops a computational model and examines its simulation results.