The first set of boxes in the spawnProjectile event control the general direction. The first is the X axis, which is towards the Door in the Bedroom or "East" to a wrench emitter when positive. The second is the Y axis, towards the poster or "North" when positive. The third is the Z axis, which is up or down.
The second set is the spread or inaccuracy - each amount is randomly added or subtracted from that in the first set for the direction.
If you set the first amount to get it in the direction you want it to go on average (using the X and Y values), then add approximately +/-10 spread in each direction, then you can get a good "rain of fire" effect.