In walking through the math to derive the equation they use in their code to maintain/model the X(t) neuron state vector I realized I was not using an appropriate time step size. After correcting the step size the model appears to make better predictions as quantified by mean Pearson Correlation Coefficient
N = 1000
214 Cells in Experiment 500964514
Using 50 cell ids: [ 7 11 26 28 40 41 45 47 49 50 54 63 68 69 70 76 77 82