I don't have a stock hood on hand and it's too long ago for me to remember, so I can't help comparatively.
On an M viewfinder at close focus (0.7m) the total outline of the 12451 takes up slightly less than a quarter of the viewfinder. The RF patch is clear of the hood outline, but the lower right 135 mm bracket is covered and the left side of the hood extends slightly past the centre of the VF. Of course you can see through the cut-out. Magnification doesn't make any difference - I just checked on 0.85 and 0.72 Ms - you just see more around the edges of the framelines, but the hood intrudes the same amount.
I don't have any other M cameras to check this on, sorry.
Marty