Fractions of WDs hosting substellar companions as function of total system age and WD Mass. The total fraction of WDs with substellar companions is 1.3% (assuming weak tides VL09, top left) and 0.6% for stronger tides according to R96. In both cases, companions are more likely around lower mass WDs and relatively young systems. In particular, for higher mass stars, stronger tides lead the radius expansion to dominate over orbital expansion, and therefore only planets around lower mass stars survive. The extension of the region with high probabilities is therefore very sensitive to the strengths of the tides. For example, further increasing the tides according to R96 by a factor of 8/3 would eliminate the remaining small high probability island in the right panel.