I'll post here too my LOS rule version (for spells+weapons) which, for me at least, solves all kinds of visibility issues.
A target is visible when you have a clear Line Of Sight from your square center to:
- their square center
(ignore 2nd occasion if target is at a diagonal square, unless LOS stops earlier; it stops at the first square after it has been touched by occupied squares from both sides)
AND - any spot (not a corner) of a side of their square
(ignore 1st occasion if target is within your M.P. area, unless a wall or high furniture cuts LOS)

Wizard may "see" Orcs 2,3 and 4 (bright squares are visible).
Elf may "see" Orcs 3,4 and 9.
Dwarf may "see" Orcs 8 and 9. Orc 5 isn't visible because LOS stops at square D.
Barbarian may only "see" the Goblin. His LOS stops at square B. Without the Goblin he would "see" Orcs 6 and 7.

Wizard may see all

but not the greenskins
(

's LOS is lost by the wall,

's LOS is lost by the warriors and it's out of Wizard's M.P. area)
Although wizard has no clear LOS
(center to center) with the Chaos Warriors, they are visible because
a) he can
see 1 side of their square
b) they are within wizard's M.P.(=6) area
and c) LOS (from center to center) is not lost by a wall or high furniture.