Rates of binarity F_bin as a function of the projected Einstein radius of the lens R_E/x, obtained for different ways of integration: from a component separation larger than R_E/x (solid red line), or larger than R_E/2x (dashed red line), or by weighting contributions with a ramp function (black line) (see text). Typical masses corresponding to the Einstein radii are plotted on the upper abscissa for sources within the LMC. This rate is an upper limit to the risk of not detecting microlensing effects due to light-curve distortion induced by binarity of sources.