An asymmetric micro-oscillator design based on a monostable fluidic amplifier is proposed. Experimental data with various feedback loop configurations point out that the main effect responsible for the oscillation is a capacitive and not a propagative effect. Actually, sound propagation in the feedback loop only generates a secondary oscillation which is not strong enough to provoke the jet switching. Data from a hybrid simulation using a commercial CFD code and a simple analytical model are in good agreement with the experimental data. A more compact plane design with reduced feedback loop volumes is also studied through a fully CFD simulation that confirms the previous conclusions.