Short Grass (and others) random position should be model property

I'm talking about that randomness that the grass has when in a block, that unlike the model, it not always in the center of the block. The suggestion is that property shouldn't be hard coded, but as a property for a cube, like this:
pos_spread: 0 (default)

And every value of pos_spread (need better name) is the amount of pixels the model is allow to disperse from his center (same distribution system as the grass), maybe also add a way to make it work also in the Y axis, if necessary