It looks ok, but maybe there is a way to make it a little bigger than one block so that it looks like one solid piece:

They each extend past the block edge by exactly 1/2 the size of the fade--so if you use a texture for the volumetrics make 25% of it faded on each side, using a square symmetrical gradient not round so there aren't dots on the corners, leaving only 50% in the middle fully opaque, but make the block in the game only scaled to 3.0/2.0 (three halves) meters or blocks so half of the fade overlaps. Usable texture (matches the ones on the right in the diagram--the ones on the left are not as good):
fog-of-war-three-halves-meter-alpha.png

or without alpha (luminosity-based mask):
fog-of-war-three-halves-meter-luma.png

According to my tests, this texture is pretty close to seamless , but corners may need to be just slightly sharper. Seeing it in game would help refine it (may be more or less seamless than test).
It looks ok, but maybe there is a way to make it a little bigger than one block so that it looks like one solid piece:
They each extend past the block edge by exactly 1/2 the size of the fade--so if you use a texture for the volumetrics make 25% of it faded on each side, using a square symmetrical gradient not round so there aren't dots on the corners, leaving only 50% in the middle fully opaque, but make the block in the game only scaled to 3.0/2.0 (three halves) meters or blocks so half of the fade overlaps. Usable texture (matches the ones on the right in the diagram--the ones on the left are not as good):
fog-of-war-three-halves-meter-alpha.png

or without alpha (luminosity-based mask):
fog-of-war-three-halves-meter-luma.png

According to my tests, this texture is pretty close to seamless , but corners may need to be just slightly sharper. Seeing it in game would help refine it (may be more or less seamless than test).