Scroll hit test area

is there a way I can control how far up and down this mouse curser script will activate the scroll, because on my website I have a menu on top and when the curser is on the menu it controls my scrolling menu below it.

cont.onEnterFrame = function() {
if (this.hitTest(_root._xmouse, _root._ymouse)) {
this._y -= _ymouse/10;
if (this._y>msk._y) {
// upper limit reached
this._y = msk._y-1;
} else if (this._y+this._height<msk._y+msk._height) {
// lower limit reached
this._y = msk._y+msk._height-this._height+1;