The Ge/Si growth process in standard stacked layers of self-assembled Ge/Si(001) islands was studied using in situ reflection high-energy electron diffraction, transmission electron microscopy and photoluminescence spectroscopy. It was found that the decrease of the Ge critical thickness in the upper layers of a stacked layer is the main parameter which leads to the increase of the upper island size and height. Such an evolution of the Ge critical thickness could be explained by an accumulation of elastic strain induced by the lower Ge islands and wetting layers in the Si spacer layers. This result opened the ways to the realization of stacked layers in which the islands have equal size in all layers even for stacked intervals being reduced down to about 1 nm.