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InGaN-based green light-emitting diodes (LEDs) with and without Mg-preflow before the growth of p-AlGaN electron blocking layer (EBL) are investigated experimentally. A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment, effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures. However, unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature. Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions. Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to p- GaN side through the c-plane rather than the V-shape pits, which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN. Within this framework, apparently disparate experimental observations regarding electroluminescence properties, in this work, are well reconciled. [ABSTRACT FROM AUTHOR]