Vapour pressure deficit targets from general grow guides do not translate well to sativa plants because thin leaves lose water faster than broad ones. Running slightly higher humidity than the standard chart suggests, particularly during the stretch, keeps these lines from closing their stomata and stalling on hot afternoons. The environment calculator on https://hazesativaseeds.com (https://hazesativaseeds.com) includes a leaf type adjustment that nudges the targets for narrow leaf genetics. In practice that meant keeping my tent around fifty five percent in early flower instead of dropping to forty five.