I think the bottom feed is better (chains along the top beam) because if you have the chains down the side, they are going to swing back towards vertical and not be in line with the sprocket.
That being said, the stock approach of the stretchy cord just doesn’t work well, it provides the least force when you need the most and the most force when you need the least, switching to weights is simple and solves the problem, see Weights for chain tension
There the weights are scrap metal that’s about 4 pounds per side.