My maths was of course wrong!- if you turn off 30 degrees from dead downwind you need to sail 14% faster to break even and if you turn off 45 degrees you need to sail 30% faster. Thus in the example I quoted where I was doing 2.8kts DDW, by turning up 30 degrees I would need to sail 3.2 knots to break even. I was actually getting 3.5 at times so maybe a small gain. Had I pointed up to 45 degrees off the DDW course I would have needed to sail at 3.64 kts to break even, which might just have been possible; but no big gain – Vmg would still have been a painful 2.8kts (give or take).
I agree that loosening the gennaker halyard helps – I have a special tackle and cleat arrangement to enable fine control of the halyard tension.
When you’ve read Asymmetric Sailing (which is not all that helpful IMHO) read Higher Performance Sailing. Do it half a chapter at a time and absorb every word!
Rgds
George Morris