This paper describes the optimisation of arrays of wave energy converters (WECs) of point absorber type. The WECs are spherical in shape and operate in heave only. Arrays of five to seven devices are considered. To simplify the optimisation, the arrays are constrained to lie in a specified geometry, namely a straight line or a circle, thereby reducing the number of array variables. The array layout is optimised from a hydrodynamic perspective with respect to the spacing or angles between the devices. Following the work of McGuinness and Thomas (Eleventh European Wave and Tidal Energy Conference. Nantes, France, 2015), the objective function of the optimisation is taken to be the mean of the interaction factor, rather than the interaction factor itself. This mean is defined over a non-dimensional length measure of the array. This is motivated by the desire to produce arrays that are stable to changes in the incident wavelength. A more general optimisation is performed here than in McGuinness and Thomas (Eleventh European Wave and Tidal Energy Conference. Nantes, France, 2015), with no prescribed symmetry in the arrays. The behaviour of the optimal arrays is analysed with respect to performance and device motions. Closely spaced groups of devices are found to exist in some of the optimal arrays; the implications of this and the possibility of replacing these groups with larger devices are discussed. For circular arrays, it is shown that the inclusion of a further device at the circle centre tends to alter the overall performance of the array. Most optimal circular arrays formed a semi-circular pattern dependent on the incident wave direction. For all array geometries considered, it is seen that the incident wave angle has a large impact on the optimal layout and the overall performance.