Toon,
In general, as you reduce the size of a patch antenna's groundplane (or the ground of any antenna that is intended to operate against it) you will observe all of the effects you mention (detuning, pattern, impedance) as well as polarization. There are some exceptions. However, given...
Try serrating the edge of an electrically small groundplane. The serrations match the field's impedance to freespace effectively making the groundplane appear electrically larger to the attached antenna. The net effect is that the antenna pattern and impedance is restored.
