Continuous-wave (CW) X-band (9. ). Spectra for 2-Yb were collected at 20 dB attenuation with 0.4 mT modulation amplitude and spectra for 4-Yb were collected at 15 dB attenuation with 0.2 mT modulation amplitude. The field was corrected using a strong pitch sample (g = 2.0028). Simulations for the 2-Yb spectrum were performed using the pepper function in EasySpin 6.0.2. Anisotropic Yb g-strains were employed to account for all anisotropic line broadening effects. Further simulation details are provided in the SI.