The chest stack size must be increased to allow construction bots to be able to build maximum possible chest with just one stack of chests.
Lower the max width, height and area mod config. Basically you should have it as low as possible while it suits your needs. You can always increase the limits when you need larger chests. For example I usually play with maximum width and height 20 and maximum area 40, which doesn't modify chest stack at all, while allowing me to merge up to 2x20 chests