A successful ionospheric electron density model assimilates relevant data for determination of its driving parameters. We process about two hours worth of two-frequency GPS ground-receiver data from five satellites in order to separate the least squares solution of up to four driving parameters of the electron density profile (EDP) model from the solution of four relative (between satellites) differential hardware biases. The EDP model we use is part of the Ionosphere and Troposphere Raytrace Model (ITRAY), which is our upgrade of the Raytrace/Ionospheric Conductivity and Electron Density model (ICED)-Bent-Gallagher (RIBG) model. We use the Westford GPS receiver in Massachusetts to update the EDP model, which we then use to predict EDP distributions at nearby Millstone Hill for comparison with ground truth incoherent-scatter radar and Digisonde data. We find that a simple procedure often works well when the model time dependence is correct, but we find that forcing the ionospheric model to more closely fit GPS data actually degrades ionospheric specification in the F layer region. We suggest a data diversification remedy.