A few things about the 1/4 ball calling. First, the longer the line, the more time a skier can spend in the 1/4 ball zone. At 15 off, the arc's potential is much longer than at 38.
Another thing, to accurately see both perspectives (ball line and boat guide line) the judge would have to be in 2 places at the same time. The steep angles and distance that the judges view the skier from make the judgement a "guess" based on their belief of where they think the skier is. It is skewed.... For example, in the sport of horse racing, no one would ever try to call a photo finish from any angle, other than standing straight across at the finish line. ANY other angle would be skewed, and would only be a guess. That's because the objects (horses) are moving quickly (i.e. the angle between the 2 is constantly changing to a single viewing point), the finish line is a straight line, the distance between the objects (horses) may vary, then, add to that an angle of someone trying to judge an exact moment, and you have quite the challenge.
God bless the judges for trying, but remember, if in doubt, give the call to the skier.