In an ideal swept frequency experiment, the electron polarization goes from +1 to -1 after a single µw pulse; thus, the polarization transfer ratio is E=2 and the surrounding N nuclear spins each gain a polarization of E/N. Furthermore, the nuclear polarization cannot be enhanced more than the electron polarization as it is the polarization difference that is transferred and oscillating. When the nuclear polarization is larger than the electron polarization, the nuclei will lose polarization to the electron. This reversal of polarization transfer is also why the ISE exhibits lower enhancement than the SSE in this regime. Theory demonstrates that the ISE has a maximum transfer ratio of 0.686, lower than 2 for the SSE, understood by realizing that a sweep through the first SE matching condition, when the DNP process is efficient, yields an electron polarization that is inverted; experimentally verification of this prediction via EPR experiments is provided in the Supporting Information. Therefore, when transitioning through the subsequent matching condition, the polarization is transferred from the nuclear spins back to the electron spin or equivalently the nuclear spins are polarized towards the other direction compared to the first matching condition. This limits the efficiency of the ISE. A video illustrating the electron and nuclear spin polarizations is provided in the supplementary information. The trajectory of the electron spin polarization vector is simulated using the SpinEvolution software 33 with 1 electron spin hyperfine coupled to 5 nuclear spins.