It occurred to me while admiring this bow, that a three piece is in addition to being a bow, is also two first order levers.
The typical style with limbs mounted on the backside, would have the fulcrum located at the end point of the riser and the load would be at the attachment bolt, pushing it outwards. The forward handle style would have the fulcrum at the attachment bolt and the load pushing into the riser block.
I'm not making an argument that one is more optimal than the other. It would be a matter of where you want the most force applied.