I agree with the others. Way too much dangle going on.
You're creating structure that is bound to flex.
Tuck it in as close as you can to avoid a hinge.
Here's what I did on my Greeves.. up front sandwiching the engine plates,
Your subframe doesn't have to be one piece, you just need four good points that will enhance and strengthen the bikes frame to create a unified structure.
Don in Nipomo