I tried anchoring the fingers the same way MAB does and it felt very uncomfortable, especially as I moved from the low strings to the higher strings. The closer my pick got to the fingers that were anchoring, it started to feel more and more cramped - I felt that the placement of the anchoring fingers got in the way of moving my wrist, that there wasn’t enough room to move my wrist the way I needed to move it.
I also found I had to bend my fingers at the knuckles more and more the closer I moved towards the high E string. When picking on the low E or A string I could keep those anchored fingers extended, but unless I bent the fingers at the knuckles, it led to my pick being way too high above the strings when I got to the B string and especially the high E string. Did you also find that anchoring that way caused those same problems?