Mass-transfer rates of the four pre-AIC binaries shown in the horizontal part of the cross in the upper panel of Fig. 3. The mass-transfer-rate from the donor star in the system with P_orb = 1.5^d is too low (see Fig. 1) to cause the accreting WD to grow sufficiently in mass and trigger an AIC event. For the donors in the other systems, on the other hand, the mass-transfer rate is too high to result in stable mass gain of the accretor. Hence, none of these models resulted in a successful AIC. The differences in these mass-transfer rates can be understood in terms of different thicknesses of convective envelopes (see text and Fig. 6).