The growth of highly strained InxGa1-xAs (x > 0.25) epitaxial layers on GaAs(001) undergoes a 2D-3D growth mode transition beyond a certain ''critical thickness''. As suggested previously, it has been found that the driving force of this transition is the strain relief by elastic deformation at the free edges of 3D islands. In fact, it is shown that this strain relaxation process is active also for 2D islands which are formed during the initial layer-by-layer growth regime. Guided by Monte Carlo growth simulations, experiments have been performed in order to increase the critical thickness at which 3D coherent island formation occurs by reducing the surface diffusion length. The reported results demonstrate that growth parameters which can be used to reduce the surface diffusion length are effective in extending the layer-by-layer growth regime of this prototypical highly strained epitaxial system.