In the case of layer-scalability, the previous MINLP formulation is superior. The new proposed formulation timed out after a few hours for a number of layers greater than four. For the function under study a three-layered tree was sufficient and the ability to discard sub-layers is in favour over constructing the whole tree with identity functions. This advantage might diminish if more complex functions are sought within higher layered trees. Applicable to both formulations, this result confirms the high computational expense of SR due to the combinatorial search space. The exponential scale-up behaviour in tree layers could strongly limit the method's ability to identify more complex models.