twist angle $\vec{\theta}=\left(\theta, \theta, \theta\right)$ such that the smallest four-momentum transfer of the current takes the value $Q^2({\rm GeV^2})=0.01841$ or $0.04237$. Adding integer momenta, we then collect data for $Q^2$ in the range $0.01841 {\rm ~GeV}^2 \leq Q^2 \leq 0.7302{\rm ~GeV}^2$. The statistics of data set I is given in Table \[table:stat\_dataset1\] together with pion and kaon mass. Results of data set I have been previously reported in [@OanhNguyen].

In order to extract the form factor, we fit the plateau of the ratio $R(\tau)$ by a constant. The fitting range should be chosen around the symmetry point between the source and the sink, with additional considerations on the time interval required for the pion state to become dominant. Since we employ an exponential smeared source and a point sink, we shift the fitting range one time unit closer to the source than the symmetric point $t_f/2=12$.

In Fig. \[fig:Plateau\_PFF\](a) we plot the ratio $R(\tau)$ at various momentum transfer for the pion mass $M_\pi \approx 702$ MeV. At this pion mass we have good signals for all 7 values of the four-momentum transfer. There is a good plateau from $\tau=8$ to 15 for every momentum transfer. Thus at this pion mass 