Never mind my previous comment... @mluessi you can make non-depth-weighted fixed inv, you just need to pass a non-`surf_ori` forward. See the weird chart here:

https://github.com/mne-tools/mne-python/blob/master/mne/minimum_norm/inverse.py#L1148

I agree some of it is convoluted. It would be nice to relax some of these requirements. I considered trying it at one point, but the code seemed too complex at the time. Now that some of the forward solution switching functions exist, it might be easier.

By the way, this was one of our old conversations on the matter @agramfort:

https://github.com/mne-tools/mne-python/pull/362/files#r2628091