In addition to the above you might want to let out your spi sheet some more to sail deeper, depending on how you usually sheet and sail of course. Build virtual wind as described, but try to carry it with you as well as you can with the spi sheeted out a bit more than usual. You can also try building virtual wind and as you fall off you sheet the spi a bit out.

Downwind sailing is an art and developing the feel for it, both in strong and weak winds takes time and hard work. Basic concept is always to build virtual wind and carry it with you as you fall back to your best course. No sailing on one hull in these conditions!