Quantum dots that store large tensile strains represent an emerging research area. We combine experiments and computational modeling to investigate the self-assembly of Ge and GaAs tensile-strained quantum dots (TSQDs) on In0.52Al0.48As(111)A. Comparing these two nominally similar material systems highlights how differences in adatom kinetics leads to distinct features of Ge and GaAs TSQD self-assembly. The energy barrier to diffusion of Ge adatoms is higher than that for Ga adatoms, while forming a stable island requires six Ge atoms and four Ga atoms. Unusually, these critical cluster sizes do not increase as we raise the substrate temperature. Radial distribution scaling shows that both Ge and GaAs TSQDs preferentially nucleate at a particular distance from their neighbors. This deeper understanding of the physics of Ge(111) and GaAs(111)A TSQD self-assembly will enable researchers to more effectively tailor these nanostructures to specific optoelectronic applications.