Sprue former should be attached to the bulkiest portion of wax because:

The sprue former should be attached to the bulkiest part of the wax pattern because of the following reasons: This will minimize the effect of released residual stresses by the heat of attaching the sprue. It will ensure that the thinner cross-section of the mold will be filled completely. The melt will always be fluid enough and available until all lesser dimension sections are adequately filled.