if you want to get the distance from the pivot of the box to the point on the accessibilty surface then you need to subtract the two y components.
remember the thing I gave you gives you a World Space position NOT a UV position (you must supply UV coordinates to get teh world space position back)

float $accessibiltyHeight[] = `pointOnSurface -u $u -v $v`;
float $boxPos[] = `xform -q -ws -t $myBox`;

float $yHeight = $boxPos[1] - $accessibiltyHeight[1];

And don't confuse maya with Artificial Intelligence... they're really not the same thing at all...


A