Do you release your main downhaul when under spinnaker? This seems to be a common recommendation and the Nacra Infusion manual says so as well: http://www.microwindracing.com/boat.html
(table down the bottom, I think it’s some kind of extract but it looks official
Interestingly Capricorn manual recommends the „same“ settings as upwind: https://www.manualslib.com/manual/750751/Ahpc-Capricorn-F18.html?page=34#manual
Any ideas why that is?