Random position moviclips again!

Hi I have a flash gave that makes a transparent movieclip appear in random positions within a set grid each time the screen loads. However I have found that a lot of the time it is always in the top left corner. I don’t know if this is just coincidence. The code I am using is.

onClipEvent(load) {
this._x = Math.random()(440.1-_width)+179.9;
this._y = Math.random()

However the grid that it appears in is covered in other moviclips. ( for the game battleships) So I was wondering if there was a way that I could say – on load appear at random behing moviclip 1 or moviclip2 or moviclip3 or moviclip4.

Or whether I could get all the positions of the moviclips which cover the grid and make it appear at random that way.

e.g appear at w90.3 x213.7
h 55.2 y 183.8
or appear at w90.3 x213.7
hh 55.2 y128.1 etc

I would be grateful for any help