When using a Firespray, often an enemy will be chasing it. That's fine, you want that.
But since the Firespray is a large base, it has to move a minimum of 3 distance forward. This means that you end up moving toward the board edge or a corner and you'll have to turn away and likely be without a shot.
You'll have to do less of this with a small base because they move one less distance.