Sensor architectures based on coupled resonators are receiving increased interest from the resonant sensing community. Certain output metrics of such sensors have an increased sensitivity to the measurand, compared to conventional resonant sensors with frequency-modulated outputs. In the present paper, we investigate the properties of a differential architecture based on mutually injection-locked oscillators beyond the linear theoretical framework, by driving the resonators higher than the critical Duffing amplitude. Our results show that a trade-off must be made between sensitivity and measurement (locking) range. Experimental results obtained with our MILO architecture and the amplitude ratio output metric are also reported for the first time.