A multi-well assembly including a filter plate and receiver plate. Each plate includes a plurality of wells, which, when the filter plate is placed in nesting relationship with the receiver plate, each filter plate well has a corresponding receiver plate well into which it extends. The receiver plate wells are of a non-uniform cross-section in order to increase the gap between the outer walls of the filter plate wells and the inner walls of a corresponding receiver plate well when the receiver plate and filter plate are in nesting relationship. The increased gap size reduces wicking and cross-contamination. A multi-section well of maximum cross-section in an upper region and a minimized cross-section in a lower region, with a gradual transition between the regions, is thus provided. The multi-well assembly of the present invention also improves the repeatability of positioning the filter plate and receiver plate in proper nesting relationship and provides stability during handling, mixing and shaking operations.