Difference between FitPercent value calculated in idpoly class and manually. (Get predicted y value in ARX function)

I want to compare accuracy of my several modeling method, arx is one of them.

So I calculate predicted y value of arx model with function 'compare'.

But when I calculate FitPercent like this documentation. https://www.mathworks.com/help/ident/ug/model-quality-metrics.html

My calculation and FitPercent value from sys.Report.Fit.FitPercent are different.

So I have 2 questions.

1. Is it right method using compare function to get predicted y value? Is there any others?

2. If calculation procedure of predicted y value is not wrong, why the NRMSE value calculated by predicted y value and sys.Report.Fit.FitPercent are different?

load iddata1

sys_armax = armax(z1,[2 3 1 0]);
[ymodel, ~, ~] = compare(z1, sys_armax);
ymodel = ymodel.y;
ymeasured = z1.y;

fit1 = goodnessOfFit(ymodel, ymeasured, 'NRMSE') % using function 'goodnessOfFit' to calculate NRMSE
fit2 = 100*(1-norm(ymeasured-ymodel)/norm(ymeasured-mean(ymeasured))) % From documentation
fit3 = sys_armax.Report.Fit.FitPercent % Get NRMSE value from idpoly class.


fit1 =

    0.7027


fit2 =

   70.2738


fit3 =

   76.0267