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This paper studies the behavior of optical feedback self-mixing interferometric (OFSMI) systems, where the semiconductor lasers operate at a single mode (perturbed external cavity mode) with a large optical feedback factor C. Based on analysis of the spectral linewidth associated with all the possible lasing modes at different C values, a set of mode jumping rules are proposed following the minimum linewidth mode competition principle proposed in . According to the rules, the C factor can be classified into different regions, on which an OFSMI system will exhibit distinct phenomena. In particular, for the same amount of displacement associated with the external cavity, the fringe number reduction on the OFSMI signal should be observed when C increases from one region to the next. An experimental setup with a laser diode HL7851G was implemented and employed to verify the proposed rules. The behavior of the OFSMI predicted by the paper has been confirmed by the experiments with C value up to 8.0.