I only used so many variables because I've been coding this over time, with no even basic plan at all on how to organize it, making it basically one big mess. I might clean it up sooner or later, but i doubt it. As for collisions, I'm using a basic hitTest:
_root.ground.hitTest(this._x, this._y+1, true)
or
_root.ground.hitTest(this._x, this._y+22, true)