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The segmented contact technique has been used to study the effects on nonradiative recombination of stacking multiple quantum-dot layers. As the number of stacked layers is increased a shift in the balance of dots in the bimodal dot distribution is observed due to a reduction in the number in the smaller dot size subset. This is attributed to an increase in the density of defect islands, as the number of layers is increased, that preferentially take material from the smaller dots, and lead to an increased level of nonradiative recombination per layer at low injection level. A second nonradiative process is apparent at higher injection level, which is related to the population of the small dot size subset. Spontaneous radiative efficiency was improved in a five-layer sample where the large to small dot size energy separation and relative density of the large dot size subset were increased.