Do you want to say how you would recommend to do it in real life?

In our work, we threshold the FA at 0.7 and mask it with a white matter mask that comes from a registered T1. This is not trivial to do for someone that is starting (need registration and segmentation tools from FSL) but it really is the optimal.

Otherwise, I recommend starting from the center of the brain, shape[0]/2, shape[1]/2, shape[2]/2, and pick 300 voxels with FA > 0.7, as recommended in Tournier et al 2007 and in Descoteaux et al TMI 2009. This way, you are sure not to pick up any high FA crap from around the brain.

Finally, I recommend to print the response and ratio, and mention that the profile must look anisotropic with a factor of approximately 5 larger first e-value than 2nd e-value. ratio needs to be in the [0.15-0.3] range. We could also render this simple one voxel response function with fvtk.

This is really where deconvolution can go wrong and a user can really mis-use it, especially if the raw data has artefacts, has been eddy, motion corrected or denoised badly....