The Entropy Wave Generator (EWG) experiment is a generic test case for indirect combustion noise. This test case was studied previously by means of experimental, analytical and numerical methods by different authors. Numerical and analytical studies show the major importance of modelling the acoustic boundary conditions to obtain accurate results for the EWG. In a previous publication, a good agreement between experimental and numerical results was achieved by means of time domain impedance boundary conditions (TDIBC). In this work, improved multirate TDIBC are presented which allow to run the CFD solver and the boundary conditions at different sampling rates. This furthermore leads to a very accurate modelling of the downstream reflection coefficient, and hence in a higher precision of the predicted indirect noise than reported in literature to date.