You can also use the drop command to enhance the appearance of your Flak. Here's a script I used to create Airburst Artillery, modified to make flak. This script will not only create a random pattern of Flak around the plane, but also leave pretty little smoke puffs behind to drift away-if you use it just give me credit somewhere in there please. Enjoy!
;Name the plane Plane1
;change _numberoflak according to how much you want
_numberoflak=25
#salvo
;get plane position
_Ppos=getpos Plane1
targetx=_Ppos select 0
targety=_Ppos select 1
_numberoflak=_numberoflak-1
;randomize bursts
_xrand=Random(80)
_yrand=Random(80)
_zrand=Random(5)
_mine="shell120" camcreate [targetx+(_xrand-40),targety+(_yrand-40),(_zrand+25)]
_mine2="shell120" camcreate [targetx+(_xrand-40),targety+(_yrand-40),(_zrand+25)]
drop ["cl_basic", "", "Billboard", 5, 5, [0, 0, 0], [0, 0, 0], 0, 1.2, 1, 0, [10,20],[[0,0,0,1],[0,0,0,0]],[0],0,0,"","",_mine]
;randomize burst interval
~random(.3)
?_n>=0:goto "salvo"
exit