My setup is similar to fig 1 of the 2nd link you posted. The engine
is mid-ship. To get the anti-siphon significantly above the waterline, they routed the in-out line for it down low in the bilge
then up into a locker. This ended up placing the anti-siphon at about 5 inches above the water
line. Less than recommended, but should work. Then the value tip of the anti-siphon has a small tube that runs back to the bilge
so no water drains into the locker. This tube is below the water line. So I guess the net affect is that the anti-siphon value acts as if it were also below the water line.