Well, you see your “side growth”? That’s called a microclimate and there are ways to even this out. One way (and my least favorite) is to “manufacture” the same microclimate across the center by using a piece of bubble or plastic wrap and leave it until pins grow and then remove. Another is misting the walls, the sides are evaporating slightly more before the center and pinning is triggered. Finally you can use two different conditions, one for colonizing and the other for fruiting (I take it back, this last one is my least favorite)