During the last years, a lot of research focusing on appropriate interfaces between substructures has been made; the transmission simulator method has become a tool in that strive. In this paper, possible sensitivity, related to ill-conditioning, of the end effects on assembled structures consisting of finite element substructure models representing experimental setups with different levels of transmission simulator mass loadings at their interfaces are studied. Here, components of the Society of Experimental Mechanics, SEM, substructuring focus group's benchmark; the Ampair A600 wind turbine, constitute the structure studied. Models of an A600 blade and bracket system attached to dummy masses of different sizes are coupled to models representing an A600 hub together with two blades attached to dummy masses of different sizes after numerical subtraction of the dummy masses on each of the substructures. The results are compared to data stemming from a model of the assembled system.