I guess you are referring to the LTE_sim_main_launcher_3D_model. The antenna spacing can be changed in both vertical and horizontal direction when using a planar antenna array. Spacing in horizontal direction refers to the distance between antenna ports, larger the distance less correlated are the channels, while spacing in vertical direction refers to the distance between antenna elements stacked to one antenna port; increasing the distance will cause a sharper beam but also granting lobes will start appearing and increase dependent on the number of antenna elements and distance. This is taken in consideration when generating the small scale fading in +channel_gain_wrappers/TR36873_Fading_3D_Channel.m, e.g. in the function calculate_channel_coefficient_OTOI() parameter element_weight changes according to the antenna element distance.
More granting lobes will increase the interference from neighboring base stations, however the overall gain/decrease in performance will depend on geometry, since when using sharps beams, if the desired base station is pointing towards the user the received signal will be higher, or when interfering BS is pointing toward the granting lobes, the interference will be high. Any combination of these situations will lead to higher/lower SINR. In general, more granting lobes, the throughput should decrease.