Look-up tables can be employed to efficiently fill Method of Moment (MoM) reaction matrices when most of the expansion and test functions have the same dimensions and are properly placed. When discretizing the signal traces into uniform length cells, there are often non-uniform length cells at the ends of the lines. Previously, these non-uniform cells were treated as two half-rooftop cells. Unfortunately, reactions with the half-rooftop cells exhibited poor convergence. Therefore, in order to overcome this convergence problem, in this paper we develop a new asymmetrical cell (A-cell), which combines the two horizontal half-rooftop cells with unequal lengths into a single cell. Since the A-cell has smoothly decaying edges, its spectrum decays faster than for the hall-rooftop cells, thus leading to a more rapid convergence of the resulting residue series. We demonstrate the new A-cells by modeling a multi-layer stripline structure and compare our results with Agilent Momentum for validation purposes.