Short lived energy-dispersed decreases of the energetic electron flux (Drifting Electron Holes, DEHs) were previously found at geostationary orbit in association with sudden onsets of intense substorms. We surveyed well-defined DEH events in the dawn LT sector observed by the CRRES spacecraft which had an eccentric equatorial orbit with 6.3 Re apogee. Eleven out of 13 events were encountered at L>6.6 Re and 10 out of 13 events were observed under quiet or weakly disturbed (AE<300nT) conditions. Comparison with particle measurements at post-midnight geostationary LANL spacecraft was possible for 6 events observed by CRRES. Only in one case, when LANL and CRRES were at the same drift shell, DEH signatures were observed at both spacecraft. In all other cases (when the CRRES L-shell was located tailward of the geostationary orbit) we observed either no associated energetic particle response at 6.6 Re, or simultaneous particle injection. The results of this limited DEH survey show that the region of DEH formation is radially localized and DEHs preferentially occur at the periphery of the radiation belt (8-10 Re). When tracing back the energy dispersed DEHs according to the electrons' magnetic drift, we found the source location always near the midnight, and, if substorm onset could be identified, in the local time sector occupied by the Substorm Current Wedge. The abovementioned facts strongly support the interpretation of DEHs as being due to the inward plasma injection from the outer boundary of the radiation belt. We suggest that the decrease of the flux is basically due to the strong flux gradient near this outer boundary.