We present a numerical model for the calculation of the opto-electronic properties of a semiconductor InAs-InAlGaAs quantum dash active material including the presence of the wetting layer (WL), formed at the bottom of the dashes, and the quantum mechanical coupling among dashes caused by the high density of the InAs islands. The model calculates self-consistently the conduction and valence band energy diagram of the confined and unconfined states, the corresponding density of states, the electron and hole wavefunctions and the gain spectra. The results obtained are also compared with a more simple model that consider dashes as isolated and without the WL. The comparison evidences the role of the WL in limiting the gain performance such as the maximum gain, the differential gain and the optical gain bandwidth. The numerical tool is then used to design an improved quantum dash material, which allows to overcome these gain limitations even in presence of the WL and the high dash density.