Question about Embedded Coder handling of tunable parameters

I have two models using data dictionaries with Simulink Parameters having storage class SimulinkGlobal. One model references the parameter from a reference model and when I build that model using Embedded Coder it is generated as a global variable with prefix "rtP_". The second model has a parameter with the same storage class but the parameter is used at the top level of the model, and when Embedded Coder generates code the parameter gets put into a structure for "parameters (auto storage)". Why the difference in behavior that depends on where the parameter is used in the model hierarchy? I dumped the model configuration settings to an M file and compared and there is no difference in the model configuration that seems to be causing the change in the generated code.