Structure-borne noise in coupled systems has been shown to be highly sensitive to joint properties. In this presentation, the effects of joint behavior is examined for coupled plates joined in the canonical L-shaped configuration. The effects of the variation of the joint properties with respect to the coordinate axis along the two-plate junction is of interest. Mid-frequency loads are used, where the modal density is not sufficiently high for standard statistical energy analysis. The problem is analyzed using several methods. A mobility approach [J. M. Cuschieri, J. Acoust. Soc. Am. 87, 1159--1165 (1990)] is used as a benchmark, which, for the thin-plate model, is exact except for mode truncation. The problem is then examined in the perspective of the following two approximate methods: a spatial and temporal averaging method using energy and intensity as the primary field variables [O. M. Bouthier and R. J. Bernhard, AIAA J. 30, 616--623 (1992)] and an asymptotic method, based on Skudrzyk's Mean Value Theory [T. Igusa and Y. Tang, AIAA J. 30, 2520--2525 (1992)]. It is found that the effects of the variations in the joint properties can be interpreted using wave vector decompositions.