[en] The ratio of electrons to negative ions extracted from Penning surface-plasma sources such as the 8X source is low even before any further steps are taken to suppress the electrons. For the 8X source the e^-/H^- ratio is typically four or five to one for H^- operation and nine to one for D^- operation. Because the coextracted e^- present a power-loading problem to the 8X-source extraction system, methods to dissipate and/or reduce the power in the e^- beam must be developed before extracting a dc H^- or D^- beam. Thus, we systematically varied the geometry of a cylindrical collar installed in the near-extraction region of the 8X source. The observed dependence of the extracted e^- and H^- currents on the collar radii and lengths suggests that a conical collar would provide superior electron suppression. The conical collar that we tested lowered the e^-/H^- ratio to 0.9/1 without reducing the extracted H^- current