Probability distribution of the orbital period and mass ratio that is predicted to be observed in the semi-detached configuration of the Case A mass transfer phase for models with accretor mass below 20 M_⊙ (top panel), 20-30 M_⊙ (middle panel) and above 30 M_⊙ (bottom panel). The grey-scale gives the probability fraction in each pixel. The total probability is normalised such that the sum over the entire area is 1.