Do they really need a headsail that overlaps the mainsail that much downwind? It seems like a piece of kit for chasing zephyrs on a lake.
We all probably oversheet our mainsails when flying spinnakers, but they seem to sacrificing any twist in the main to keep tension on the forestay.
With that big a slot, you are gonna have to keep the mainsail flat to stop it chocking
With a smaller downwind head sail, they could have a bit of camber and twist in the main which would take away the aggressive helming.

Geeeez, The rubbish that keeps me awake at night........................