The high efficiency of fast adiabatic transfer for 13 C2-maleic acid in less than 1 s results from magnetic nonequivalence of the AA'X spin system comprising the two pH2 derived protons and the C nucleus in ULF. The situation is different for 13 C2-fumarate, the trans-isomer of maleate, with a spin system that features weak magnetic non-equivalence of the protons. In this case, as was thoroughly studied in , a linear field sweep in a similar experimental protocol requires a sweep duration of at least 3 s to reach maximal transfer efficiency. It was also demonstrated that an optimal rather than a linear field variation allows shortening the transfer process by taking into account the structure of the relevant LACs. In the discussed case, the optimization routine stems from the concept of a general adiabaticity factor that indicates the optimal rate of the field variation at a given ULF. This method has demonstrated its advantages in adiabatic manipulations with singlet order both at high and ultralow 33 magnetic fields. However, to precisely calculate such a constant adiabaticity profile, one must carry out a detailed theoretical analysis, including the identification of all LACs relevant for the transfer process and all the states initially populated in the given experimental scheme. This task, which is feasible in a three-spin system, becomes impractical for multi-spin systems, especially when many J-couplings are on the same order of magnitude.