In biological and artificial adhesive systems, the lowest-scale unit is oftentimes the adhesive contact between a mushroom-shaped fiber and the surrounding material. Contact mechanics analysis in literature suggests that such a shape leads to more uniform interface stress, and thus a more superior adhesive performance, than the cylindrical fiber. In this work, we prove that this concept only works in the limit of linear elastic fracture mechanics (LEFM). When the interface behavior has a large crack bridging zone, de-adhesion occurs more easily in the center of mushroom-shaped indenter and the pull-off force becomes lower than that of cylindrical fiber. Combining the analysis of stress intensity factor and crack bridging characteristics, and tuning the substrate by a layered structure, we have established design rules that can significantly widen the parametric space in which the mushroom-shaped indenter enhances the bio-adhesive performance.