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Harmonic cavities (HCs) are widely used in electron storage rings, mainly to increase the Touschek lifetime by lengthening bunches. HCs have become critical components of almost all fourth-generation synchrotron light sources. In addition to the benefits of increasing the Touschek lifetime, they also affect the collective beam instabilities in electron storage rings. However, the influence of HC settings on collective beam instabilities is still not well understood. HCs are typically designed to operate under so-called ideal lengthening conditions, which do not necessarily optimize the suppression of collective beam instabilities. We therefore extended earlier studies of collective beam instabilities to consider more general HC settings. We present preliminary studies and analyses of the influences of different HC settings on microwave and transverse mode-coupling instabilities.