The three main options for transferring polarization at an avoided level crossing are (i) adiabatic passage through LAC by slow magnetic field variation and (ii) coherent exchange induced by instantaneous field switching, and (iii) carrying out hydrogenation directly at the LAC field. In the first two approaches, we start by preparing proton singlet order in a field that does not match the LAC condition, e.g., a least a few tens of µT (Fig. .b), before performing field switching, either instant or adiabatic. In case (iii), the coherent singlet order transfer occurs concurrently with formation of the product molecules. To calculate the resulting spin order, one needs to average/integrate the density matrix over the reaction period, which usually lasts a few seconds . This leads to a partial decay of coherences, making this approach somewhat similar to the high-field PASADENA experiment. We consider this type of PHIP to be the most straightforward, since the strength of the magnetic field is the only adjustable experimental parameter. The maximum polarization transfer occurs at the magnetic field corresponding to LAC of the spin system in the product molecule. For simple spin systems, it is possible to calculate the LAC positions analytically, but in larger spin systems with several LACs one has to either calculate the field dependence numerically, or measure it experimentally. In the present work, we demonstrate a facile and convenient route to transform such field dependence into an optimal field sweep that provides the best C polarization in multi-nuclear spin systems. To optimize the performance of such PHIP transfer experiments we start by studying the field dependence of the resulting C polarization. The corresponding experimental protocol 1 (Fig. .b) includes: (1) continuous pH2 bubbling at field 𝐵 𝑈𝐿𝐹 for time 𝜏 𝑏𝑢𝑏𝑙 , which is here equal to the evolution period at the ultralow magnetic field 𝜏 𝑈𝐿𝐹 , (2) instant field jump to an intermediate field 𝐵 𝑗𝑢𝑚𝑝 , (3) sample transfer to the detection zone, and (4) C NMR detection with a hard 90 pulse. The value of field 𝐵 𝑗𝑢𝑚𝑝 was set equal to 50 uT, which is above any possible LAC field for the relevant molecules (Fig. .a). This ensures that an instant field jump induces a completely diabatic transition from the LAC field to high field, which increases the reproducibility of the experiment and simplifies the calculations.