In steady-state proton–boron (p-B) fusion systems, achieving optimistic fusion power with limited auxiliary heating power is a prerequisite for net energy gain. The non-Maxwellian proton distribution (NMPD) with a high-energy tail tuned to the peak of the p-B fusion cross-section can enhance fusion reactions but requires recirculating power to maintain, a critical yet underexplored trade-off. To quantitatively evaluate this, we develop a zero-dimensional kinetic model based on Rider’s theoretical framework (Rider 1997 Physics of Plasmas4 1039). The model solves the Fokker–Planck equation under conditions of spatial homogeneity and isotropy, focusing solely on collisional effects. As an optimistic theoretical benchmark, our analysis reveals that: (1) when proton distribution evolution is dominated by proton–proton collisions, maintaining a tailored NMPD could potentially reduce the energy confinement time required for by up to with ion equivalent temperature keV compared to an equivalent Maxwellian plasma assuming recirculating power is ideally offset by auxiliary heating; if fully optimally offset by fusion self-heating, it can enhance the fusion power by at keV and reduce the required energy confinement time for ignition by an order of magnitude. (2) Considering effect of proton-others collisions (protons, electrons, boron ions, and particles), the recirculating power density required to sustain the distribution-when inter-species collisions are included-is 2–3 times higher than that from proton–proton collisions alone. Within this idealized framework, our work provides a systematic evaluation of the fusion reactivity enhancement enabled by the NMPD against the recirculating power required to sustain them, establishing a lower limit for the difficulty of achieving p-B fusion, noting that realistic engineering requirements for ignition are likely to be more stringent.