Question about loading with an SUT

From my understanding, when using a SUT, gain tends to play a more critical role than loading.

That said, if you're already getting great sound from both cartridges with the same SUT, I wouldn't worry about it as mentioned by others. By the way, you didn’t mention which phono stage you’re pairing with your setup.

I have a DL-103R feeding into a Cinemag 3440 with switchable taps for 1:18 (150 ohm) or 1:36 (37.5 ohm). I use 1:18 and it sounds lovely. I also have a Rothwell MCL with 1:20 (100 ohm) and I honestly can't hear a difference between these two SUTs. I've switched back and forth many times and settled on the Cinemag. 

The 1:36 ratio with the Denon cartridge gives you an impedance that the Denon cannot drive efficiently. About 50% of its signal voltage output will be lost to ground. So doubling the turns ratio from 1:18 to 1:36 gives you nothing in terms of added gain. In addition at the higher ratio the treble may roll off due to the effect of capacitance. My point being that with a SUT, impedance as affected by turns ratio is every bit as important as voltage gain, and it’s usually a trade off.

I have a Zesto SUT with adjustable ratios and loadings going into a EAT eglo petite also with adjustable gain and loadings for an Aphelion2 cart (and previously a Soundsmith Zephyr MIMC*). In both cases the recommended loadings sounded best to my ears. Differences between settings are extraordinarily subtle to zero, so only major mismatches made a clear difference. In your case, the recommended and available values are very close, so as others have said, don't worry about it. 

I just realized the 103R has an internal resistance of 14 ohms, as compared to the standard DL103 with R = ~30 ohms. Therefore I have to temper my earlier advice. Setting the SUT ratio at 1:36 would still be suboptimal but not as bad as I indicated. Ideally you want the output impedance, in this case the internal R, to be at least one tenth of the input impedance of in this case the phono stage. A higher ratio is fine. At lower ratios more and more of the cartridge output is lost to ground. When the two impedances are equal, 50% of the signal is lost.