In this paper we study the problem of homothety’s influence on the number of optimal design support points under fixed values of a regression model’s parameters. The Cobb–Douglas two-dimensional nonlinear in parameters model used in microeconomics is considered. There exist two types of optimal designs: saturated (i.e. design with the number support points equal to the number of parameters) and excess design (i.e. design with greater number of support points). The optimal designs with the minimal number of support points are constructed explicitly. Numerical methods for constructing designs with greater number of points are used.