Trouble with code

1

Flash 8 AS2
Hey, what i am trying to do is get a movieclip head towards another movieclip when it hitTests with a certain radius (have a movieclip for radius) and this is my code
50% of it works, although when aproaching one mc from the other side it rejects it instead of heading towards the mc

function ai1() {
    var _s1:Number = enemy_mc._x-hero_mc._x;
    var _s2:Number = enemy_mc._y-hero_mc._y;
    var _k:Number = _s1/_s2;
    var _speed:Number = 5;
    enemy_mc.onEnterFrame = function():Void  {
        if (_root.enemy_mc.radius.hitTest(_root.hero_mc.heroh)) {
            this._x += _speed;
            this._y += _speed/_k;
        }
    };
}