How to analyze the current-induced forces after transiesta calculation?

Through literature review, I learned that it is possible to calculate the current-indeced forces on atoms where in the scattering region(SR) when bias is applied with transiesta calculation.
I used pure metal as the electrode for calculation, and use the supercell of electrode for calculation of transiesta.
I have encountered some questions about the use and post-processing of transiesta
Problem 1. Charge dQ is difficult to converge.
Even though the system I used was pure metal, dQ was surprisingly difficult to converge. Therefore, I construct the geometric model of electrode -buffer region-scattering region- buffer region- electrode for calculation. This model makes dQ converge well. But I don’t know if this is the right setting.
Question 2. Analysis of forces
First, I find that in the calculation of bias=0V, the force on the atoms in the scattering region in the output ".tsfa “file is the same as that in the output”.fa "file of siesta. Does this mean that when I analyze the calculation for bias=0.2V, the actual force of the atom should be the difference between the result for bias=0.2V and the result for bias=0V?
Secondly, since buffer reigon was introduced in the previous calculation, I tested the force of scattered regions atom in the same geometric structure when buffer regions with different thicknesses. I found that when buffer regions with different thicknesses , The force on the same atom changes the direction (not just the magnitude). So this leaves me a little confused, i how do I do to get the real forces? According to the manual, is only the core atoms of the scattering region should be considered to analyze the force.
Question 3. Post-processing the transiesta output file
transiesta outputs quite a lot of files, but I found that I didn’t have a good guide for post-processing. How to plot the electron scattering charge density or current-induced electron number density variations in Real space?
The files used in the calculation have been uploaded.
Any help would be greatly appreciated!!!

elec.fdf (2.6 KB)
scat.fdf (6.6 KB)