Experimental studies on the reflection and transmission of bounded acoustic beams at a liquid–solid plate–liquid interface show that, for incidences at or near the Lamb angles, some effects occur which are similar to those reported at a liquid–solid interface for the Rayleigh incidence. Theoretical descriptions of this phenomenon have been proposed that are based upon asymptotic considerations for the reflected beam and numerical considerations for the reflected and the transmitted beams. These previous theories are extended in this work. The reflected and transmitted Gaussian beams are described through a short wave asymptotic analysis in regions which are not restricted to the interfaces. The nonspecular effects which appear in the transmitted field composition are different according to whether the Lamb mode under consideration is symmetric or antisymmetric. The particular case when two Lamb modes are simultaneously excited is also studied. If the two modes have a different nature, the nonspecular effects are added while, for two modes of same nature (symmetric or antisymmetric), this is no longer true.