Storage size is kind-of configurable now—there's a startup setting from 0.2.0 onwards to use the capacities from 0.1.x (Factorio 0.16), now that the warehouse/storehouse capacities were rebalanced.
I thought about adding a numerical setting for complete control, but decided that it would add too much setting complexity at once. (0.2.0 added three settings already; maybe I'll reconsider this for a future version.)