[Ziegelsteinfaust]

Bag 1/2-2/3 way down the top bar is the best ride. Load capacity is decreased due to mentioned bending of the bar, but if your bars are thick enough not a problem. If you go further down the bar to say 3/4 it does improve load capacity, but ride suffers. Also you'll need limit straps to keep the axle from dropping to far.

Bag over axle carries the most, and typically has the roughest ride. This can be tamed by playing with bag height, bag diameter, and type or sub-type of bag used.

Bag behind axle rides better from what I have read. I just can't wrap my head onto how.

I think your bars are to short for Bag on Bar set-ups unless you run the bars inside the frame rails when you run wider tires.