Yep, 100% fine! That’s the very purpose of this algorithm even.
Nope! That would actually be wrong in certain ways; you’d get a multi-shell response in the end that’s a combination of single-shell responses from different sources (voxels in this case), something you definitely don’t want to have for various reasons.
dwi2response dhollander was designed for any number of b-values. The new 2019 version (which you’re probably not using here yet) even improves the single-fibre WM response estimation in particular for multiple b-values. (sources: ISMRM abstract and ISMRM talk)
If you’d like me to have a look just to be sure, happily post the contents of your estimated WM, GM and CSF response functions here. You can also get an image of the final voxel selection via the
-voxels option. Here’s an old post on how you can visualise these voxels easily for inspection.
All the best,